diff --git a/analytics/tests/test_stats_views.py b/analytics/tests/test_stats_views.py
index 7e85ec0b48..e4da601875 100644
--- a/analytics/tests/test_stats_views.py
+++ b/analytics/tests/test_stats_views.py
@@ -306,7 +306,7 @@ class TestGetChartData(ZulipTestCase):
             },
             subdomain="zephyr",
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_include_empty_subgroups(self) -> None:
         FillState.objects.create(
diff --git a/zerver/actions/streams.py b/zerver/actions/streams.py
index 115519dd95..618ba1ca88 100644
--- a/zerver/actions/streams.py
+++ b/zerver/actions/streams.py
@@ -114,7 +114,7 @@ def send_user_remove_events_on_stream_deactivation(
 def do_deactivate_stream(stream: Stream, *, acting_user: Optional[UserProfile]) -> None:
     # If the stream is already deactivated, this is a no-op
     if stream.deactivated is True:
-        raise JsonableError(_("Stream is already deactivated"))
+        raise JsonableError(_("Channel is already deactivated"))
 
     # We want to mark all messages in the to-be-deactivated stream as
     # read for all users; otherwise they will pollute queries like
@@ -238,10 +238,10 @@ def do_unarchive_stream(
 ) -> None:
     realm = stream.realm
     if not stream.deactivated:
-        raise JsonableError(_("Stream is not currently deactivated"))
+        raise JsonableError(_("Channel is not currently deactivated"))
     if Stream.objects.filter(realm=realm, name=new_name).exists():
         raise JsonableError(
-            _("Stream named {channel_name} already exists").format(channel_name=new_name)
+            _("Channel named {channel_name} already exists").format(channel_name=new_name)
         )
     assert stream.recipient_id is not None
 
diff --git a/zerver/lib/email_mirror.py b/zerver/lib/email_mirror.py
index b27e3b4cdf..999c6ea4e9 100644
--- a/zerver/lib/email_mirror.py
+++ b/zerver/lib/email_mirror.py
@@ -6,6 +6,7 @@ from email.message import EmailMessage
 from typing import Dict, List, Match, Optional, Tuple
 
 from django.conf import settings
+from django.utils.translation import gettext as _
 from typing_extensions import override
 
 from zerver.actions.message_send import (
@@ -205,7 +206,9 @@ def send_mm_reply_to_stream(
             message_content=body,
         )
     except JsonableError as error:
-        error_message = f"Error sending message to stream {stream.name} via message notification email reply:\n{error.msg}"
+        error_message = _(
+            "Error sending message to channel {channel_name} via message notification email reply:\n{error_message}"
+        ).format(channel_name=stream.name, error_message=error.msg)
         internal_send_private_message(
             get_system_bot(settings.NOTIFICATION_BOT, user_profile.realm_id),
             user_profile,
diff --git a/zerver/lib/streams.py b/zerver/lib/streams.py
index 913e223dd9..8ed39edaca 100644
--- a/zerver/lib/streams.py
+++ b/zerver/lib/streams.py
@@ -239,21 +239,21 @@ def check_stream_access_based_on_stream_post_policy(sender: UserProfile, stream:
     if sender.is_realm_admin or is_cross_realm_bot_email(sender.delivery_email):
         pass
     elif stream.stream_post_policy == Stream.STREAM_POST_POLICY_ADMINS:
-        raise JsonableError(_("Only organization administrators can send to this stream."))
+        raise JsonableError(_("Only organization administrators can send to this channel."))
     elif (
         stream.stream_post_policy == Stream.STREAM_POST_POLICY_MODERATORS
         and not sender.is_moderator
     ):
         raise JsonableError(
-            _("Only organization administrators and moderators can send to this stream.")
+            _("Only organization administrators and moderators can send to this channel.")
         )
     elif stream.stream_post_policy != Stream.STREAM_POST_POLICY_EVERYONE and sender.is_guest:
-        raise JsonableError(_("Guests cannot send to this stream."))
+        raise JsonableError(_("Guests cannot send to this channel."))
     elif (
         stream.stream_post_policy == Stream.STREAM_POST_POLICY_RESTRICT_NEW_MEMBERS
         and sender.is_provisional_member
     ):
-        raise JsonableError(_("New members cannot send to this stream."))
+        raise JsonableError(_("New members cannot send to this channel."))
 
 
 def access_stream_for_send_message(
@@ -313,22 +313,25 @@ def access_stream_for_send_message(
 
     # All other cases are an error.
     raise JsonableError(
-        _("Not authorized to send to stream '{channel_name}'").format(channel_name=stream.name)
+        _("Not authorized to send to channel '{channel_name}'").format(channel_name=stream.name)
     )
 
 
 def check_for_exactly_one_stream_arg(stream_id: Optional[int], stream: Optional[str]) -> None:
     if stream_id is None and stream is None:
-        raise JsonableError(_("Please supply 'stream'."))
+        # Uses the same translated string as RequestVariableMissingError
+        # with the stream_id parameter, which is the more common use case.
+        error = _("Missing '{var_name}' argument").format(var_name="stream_id")
+        raise JsonableError(error)
 
     if stream_id is not None and stream is not None:
-        raise JsonableError(_("Please choose one: 'stream' or 'stream_id'."))
+        raise JsonableError(_("Please supply only one channel parameter: name or ID."))
 
 
 def check_stream_access_for_delete_or_update(
     user_profile: UserProfile, stream: Stream, sub: Optional[Subscription] = None
 ) -> None:
-    error = _("Invalid stream ID")
+    error = _("Invalid channel ID")
     if stream.realm_id != user_profile.realm_id:
         raise JsonableError(error)
 
@@ -347,7 +350,7 @@ def access_stream_for_delete_or_update(
     try:
         stream = Stream.objects.get(id=stream_id)
     except Stream.DoesNotExist:
-        raise JsonableError(_("Invalid stream ID"))
+        raise JsonableError(_("Invalid channel ID"))
 
     try:
         sub = Subscription.objects.get(
@@ -430,7 +433,7 @@ def access_stream_by_id(
     require_active: bool = True,
     allow_realm_admin: bool = False,
 ) -> Tuple[Stream, Optional[Subscription]]:
-    error = _("Invalid stream ID")
+    error = _("Invalid channel ID")
     try:
         stream = get_stream_by_id_in_realm(stream_id, user_profile.realm)
     except Stream.DoesNotExist:
@@ -472,9 +475,7 @@ def check_stream_name_available(realm: Realm, name: str) -> None:
     check_stream_name(name)
     try:
         get_stream(name, realm)
-        raise JsonableError(
-            _("Stream name '{channel_name}' is already taken.").format(channel_name=name)
-        )
+        raise JsonableError(_("Channel name already in use."))
     except Stream.DoesNotExist:
         pass
 
@@ -482,7 +483,7 @@ def check_stream_name_available(realm: Realm, name: str) -> None:
 def access_stream_by_name(
     user_profile: UserProfile, stream_name: str, allow_realm_admin: bool = False
 ) -> Tuple[Stream, Optional[Subscription]]:
-    error = _("Invalid stream name '{channel_name}'").format(channel_name=stream_name)
+    error = _("Invalid channel name '{channel_name}'").format(channel_name=stream_name)
     try:
         stream = get_realm_stream(stream_name, user_profile.realm_id)
     except Stream.DoesNotExist:
@@ -498,7 +499,7 @@ def access_stream_by_name(
 
 
 def access_web_public_stream(stream_id: int, realm: Realm) -> Stream:
-    error = _("Invalid stream ID")
+    error = _("Invalid channel ID")
     try:
         stream = get_stream_by_id_in_realm(stream_id, realm)
     except Stream.DoesNotExist:
@@ -602,7 +603,7 @@ def can_access_stream_history(user_profile: UserProfile, stream: Stream) -> bool
 
     if stream.is_history_public_to_subscribers():
         # In this case, we check if the user is subscribed.
-        error = _("Invalid stream name '{channel_name}'").format(channel_name=stream.name)
+        error = _("Invalid channel name '{channel_name}'").format(channel_name=stream.name)
         try:
             access_stream_common(user_profile, stream, error)
         except JsonableError:
@@ -747,11 +748,11 @@ def list_to_streams(
             if is_default_stream and not user_profile.is_realm_admin:
                 raise JsonableError(_("Insufficient permission"))
             if invite_only and is_default_stream:
-                raise JsonableError(_("A default stream cannot be private."))
+                raise JsonableError(_("A default channel cannot be private."))
 
         if not autocreate:
             raise JsonableError(
-                _("Stream(s) ({channel_names}) do not exist").format(
+                _("Channel(s) ({channel_names}) do not exist").format(
                     channel_names=", ".join(
                         stream_dict["name"] for stream_dict in missing_stream_dicts
                     ),
@@ -760,7 +761,7 @@ def list_to_streams(
 
         if web_public_stream_requested:
             if not user_profile.realm.web_public_streams_enabled():
-                raise JsonableError(_("Web-public streams are not enabled."))
+                raise JsonableError(_("Web-public channels are not enabled."))
             if not user_profile.can_create_web_public_streams():
                 # We set create_web_public_stream_policy to allow only organization owners
                 # to create web-public streams, because of their sensitive nature.
@@ -790,7 +791,9 @@ def access_default_stream_group_by_id(realm: Realm, group_id: int) -> DefaultStr
         return DefaultStreamGroup.objects.get(realm=realm, id=group_id)
     except DefaultStreamGroup.DoesNotExist:
         raise JsonableError(
-            _("Default stream group with id '{group_id}' does not exist.").format(group_id=group_id)
+            _("Default channel group with id '{group_id}' does not exist.").format(
+                group_id=group_id
+            )
         )
 
 
diff --git a/zerver/openapi/zulip.yaml b/zerver/openapi/zulip.yaml
index 29d2636e78..1c42b1199f 100644
--- a/zerver/openapi/zulip.yaml
+++ b/zerver/openapi/zulip.yaml
@@ -5139,7 +5139,7 @@ paths:
                   - example:
                       {
                         "code": "BAD_REQUEST",
-                        "msg": "Invalid stream name 'nonexistent'",
+                        "msg": "Invalid channel name 'nonexistent'",
                         "result": "error",
                       }
                     description: |
@@ -6041,7 +6041,7 @@ paths:
                       - example:
                           {
                             "code": "BAD_REQUEST",
-                            "msg": "Private streams cannot be made default.",
+                            "msg": "Private channels cannot be made default.",
                             "result": "error",
                           }
                         description: |
@@ -9469,7 +9469,7 @@ paths:
                   - $ref: "#/components/schemas/CodedError"
                   - example:
                       {
-                        "msg": "Unable to access stream (private_stream).",
+                        "msg": "Unable to access channel (private).",
                         "result": "error",
                         "code": "BAD_REQUEST",
                       }
@@ -21281,7 +21281,7 @@ components:
             code: {}
           example:
             {
-              "msg": "Invalid stream ID",
+              "msg": "Invalid channel ID",
               "code": "BAD_REQUEST",
               "result": "error",
             }
diff --git a/zerver/tests/test_bots.py b/zerver/tests/test_bots.py
index fb89ac5a84..3ee1b3bf92 100644
--- a/zerver/tests/test_bots.py
+++ b/zerver/tests/test_bots.py
@@ -472,7 +472,7 @@ class BotTest(ZulipTestCase, UploadSerializeMixin):
             "default_sending_stream": "Denmark",
         }
         result = self.client_post("/json/bots", bot_info)
-        self.assert_json_error(result, "Invalid stream name 'Denmark'")
+        self.assert_json_error(result, "Invalid channel name 'Denmark'")
 
     def test_add_bot_with_default_events_register_stream(self) -> None:
         bot_email = "hambot-bot@zulip.testserver"
@@ -556,7 +556,7 @@ class BotTest(ZulipTestCase, UploadSerializeMixin):
             "default_events_register_stream": "Denmark",
         }
         result = self.client_post("/json/bots", bot_info)
-        self.assert_json_error(result, "Invalid stream name 'Denmark'")
+        self.assert_json_error(result, "Invalid channel name 'Denmark'")
 
     def test_add_bot_with_default_all_public_streams(self) -> None:
         self.login("hamlet")
@@ -1403,7 +1403,7 @@ class BotTest(ZulipTestCase, UploadSerializeMixin):
         }
         email = "hambot-bot@zulip.testserver"
         result = self.client_patch(f"/json/bots/{self.get_bot_user(email).id}", bot_info)
-        self.assert_json_error(result, "Invalid stream name 'Denmark'")
+        self.assert_json_error(result, "Invalid channel name 'Denmark'")
 
     def test_patch_bot_to_stream_not_found(self) -> None:
         self.login("hamlet")
@@ -1418,7 +1418,7 @@ class BotTest(ZulipTestCase, UploadSerializeMixin):
         }
         email = "hambot-bot@zulip.testserver"
         result = self.client_patch(f"/json/bots/{self.get_bot_user(email).id}", bot_info)
-        self.assert_json_error(result, "Invalid stream name 'missing'")
+        self.assert_json_error(result, "Invalid channel name 'missing'")
 
     def test_patch_bot_events_register_stream(self) -> None:
         hamlet = self.example_user("hamlet")
@@ -1453,7 +1453,7 @@ class BotTest(ZulipTestCase, UploadSerializeMixin):
         self.subscribe(bot_user, stream_name)
         bot_info = dict(default_events_register_stream=stream_name)
         result = self.client_patch(url, bot_info)
-        self.assert_json_error_contains(result, "Invalid stream name")
+        self.assert_json_error_contains(result, "Invalid channel name")
 
         # Subscribing the owner allows us to patch the stream.
         self.subscribe(hamlet, stream_name)
@@ -1520,7 +1520,7 @@ class BotTest(ZulipTestCase, UploadSerializeMixin):
         }
         email = "hambot-bot@zulip.testserver"
         result = self.client_patch(f"/json/bots/{self.get_bot_user(email).id}", bot_info)
-        self.assert_json_error(result, "Invalid stream name 'Denmark'")
+        self.assert_json_error(result, "Invalid channel name 'Denmark'")
 
     def test_patch_bot_events_register_stream_none(self) -> None:
         self.login("hamlet")
@@ -1560,7 +1560,7 @@ class BotTest(ZulipTestCase, UploadSerializeMixin):
         }
         email = "hambot-bot@zulip.testserver"
         result = self.client_patch(f"/json/bots/{self.get_bot_user(email).id}", bot_info)
-        self.assert_json_error(result, "Invalid stream name 'missing'")
+        self.assert_json_error(result, "Invalid channel name 'missing'")
 
     def test_patch_bot_default_all_public_streams_true(self) -> None:
         self.login("hamlet")
diff --git a/zerver/tests/test_drafts.py b/zerver/tests/test_drafts.py
index b69b6a6780..2ddfb0a811 100644
--- a/zerver/tests/test_drafts.py
+++ b/zerver/tests/test_drafts.py
@@ -255,7 +255,7 @@ class DraftCreationTests(ZulipTestCase):
                 "timestamp": 1595479019,
             }
         ]
-        self.create_and_check_drafts_for_error(draft_dicts, "Invalid stream ID")
+        self.create_and_check_drafts_for_error(draft_dicts, "Invalid channel ID")
 
         # When the stream itself does not exist:
         draft_dicts = [
@@ -267,7 +267,7 @@ class DraftCreationTests(ZulipTestCase):
                 "timestamp": 1595479019,
             }
         ]
-        self.create_and_check_drafts_for_error(draft_dicts, "Invalid stream ID")
+        self.create_and_check_drafts_for_error(draft_dicts, "Invalid channel ID")
 
     def test_create_personal_message_draft_for_non_existing_user(self) -> None:
         draft_dicts = [
diff --git a/zerver/tests/test_email_mirror.py b/zerver/tests/test_email_mirror.py
index b02f17bbd3..855836587a 100644
--- a/zerver/tests/test_email_mirror.py
+++ b/zerver/tests/test_email_mirror.py
@@ -1174,7 +1174,7 @@ class TestMissedMessageEmailMessages(ZulipTestCase):
 
         self.assertEqual(
             message.content,
-            "Error sending message to stream announce via message notification email reply:\nOnly organization administrators can send to this stream.",
+            "Error sending message to channel announce via message notification email reply:\nOnly organization administrators can send to this channel.",
         )
         self.assertEqual(
             message.sender,
diff --git a/zerver/tests/test_example.py b/zerver/tests/test_example.py
index 850f44561b..2c2a1e6787 100644
--- a/zerver/tests/test_example.py
+++ b/zerver/tests/test_example.py
@@ -292,7 +292,7 @@ class TestStreamHelpers(ZulipTestCase):
         access_stream_for_send_message(cordelia, stream, forwarder_user_profile=None)
 
         # ...but Othello can't.
-        with self.assertRaisesRegex(JsonableError, "Not authorized to send to stream"):
+        with self.assertRaisesRegex(JsonableError, "Not authorized to send to channel"):
             access_stream_for_send_message(othello, stream, forwarder_user_profile=None)
 
 
diff --git a/zerver/tests/test_message_flags.py b/zerver/tests/test_message_flags.py
index b242262832..72f54ff304 100644
--- a/zerver/tests/test_message_flags.py
+++ b/zerver/tests/test_message_flags.py
@@ -590,7 +590,7 @@ class UnreadCountTests(ZulipTestCase):
                 "stream_id": invalid_stream_id,
             },
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_mark_all_topics_unread_with_invalid_stream_name(self) -> None:
         self.login("hamlet")
@@ -602,7 +602,7 @@ class UnreadCountTests(ZulipTestCase):
                 "topic_name": "whatever",
             },
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_mark_all_in_stream_topic_read(self) -> None:
         self.login("hamlet")
diff --git a/zerver/tests/test_message_move_stream.py b/zerver/tests/test_message_move_stream.py
index 880bad4cfe..607b79f756 100644
--- a/zerver/tests/test_message_move_stream.py
+++ b/zerver/tests/test_message_move_stream.py
@@ -394,7 +394,7 @@ class MessageMoveStreamTest(ZulipTestCase):
             },
         )
 
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_move_message_realm_admin_cant_move_to_private_stream_without_subscription(
         self,
@@ -414,7 +414,7 @@ class MessageMoveStreamTest(ZulipTestCase):
             },
         )
 
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_move_message_realm_admin_cant_move_from_private_stream_without_subscription(
         self,
@@ -1000,7 +1000,7 @@ class MessageMoveStreamTest(ZulipTestCase):
         do_change_stream_post_policy(
             new_stream, Stream.STREAM_POST_POLICY_ADMINS, acting_user=user_profile
         )
-        error_msg = "Only organization administrators can send to this stream."
+        error_msg = "Only organization administrators can send to this channel."
         check_move_message_to_stream(UserProfile.ROLE_MODERATOR, error_msg)
         check_move_message_to_stream(UserProfile.ROLE_REALM_ADMINISTRATOR)
 
@@ -1012,7 +1012,7 @@ class MessageMoveStreamTest(ZulipTestCase):
         do_change_stream_post_policy(
             new_stream, Stream.STREAM_POST_POLICY_MODERATORS, acting_user=user_profile
         )
-        error_msg = "Only organization administrators and moderators can send to this stream."
+        error_msg = "Only organization administrators and moderators can send to this channel."
         check_move_message_to_stream(UserProfile.ROLE_MEMBER, error_msg)
         check_move_message_to_stream(UserProfile.ROLE_MODERATOR)
 
@@ -1024,7 +1024,7 @@ class MessageMoveStreamTest(ZulipTestCase):
         do_change_stream_post_policy(
             new_stream, Stream.STREAM_POST_POLICY_RESTRICT_NEW_MEMBERS, acting_user=user_profile
         )
-        error_msg = "New members cannot send to this stream."
+        error_msg = "New members cannot send to this channel."
 
         do_set_realm_property(
             user_profile.realm, "waiting_period_threshold", 100000, acting_user=None
diff --git a/zerver/tests/test_message_send.py b/zerver/tests/test_message_send.py
index 24ace18241..0ba9464342 100644
--- a/zerver/tests/test_message_send.py
+++ b/zerver/tests/test_message_send.py
@@ -268,7 +268,7 @@ class MessagePOSTTest(ZulipTestCase):
         self._send_and_verify_message(
             non_admin_profile,
             stream_name,
-            "Only organization administrators can send to this stream.",
+            "Only organization administrators can send to this channel.",
         )
         non_admin_owned_bot = self.create_test_bot(
             short_name="whatever2",
@@ -278,7 +278,7 @@ class MessagePOSTTest(ZulipTestCase):
         self._send_and_verify_message(
             non_admin_owned_bot,
             stream_name,
-            "Only organization administrators can send to this stream.",
+            "Only organization administrators can send to this channel.",
         )
 
         moderator_profile = self.example_user("shiva")
@@ -288,7 +288,7 @@ class MessagePOSTTest(ZulipTestCase):
         self._send_and_verify_message(
             moderator_profile,
             stream_name,
-            "Only organization administrators can send to this stream.",
+            "Only organization administrators can send to this channel.",
         )
         moderator_owned_bot = self.create_test_bot(
             short_name="whatever3",
@@ -298,7 +298,7 @@ class MessagePOSTTest(ZulipTestCase):
         self._send_and_verify_message(
             moderator_owned_bot,
             stream_name,
-            "Only organization administrators can send to this stream.",
+            "Only organization administrators can send to this channel.",
         )
 
         # Bots without owner (except cross realm bot) cannot send to announcement only streams
@@ -313,7 +313,7 @@ class MessagePOSTTest(ZulipTestCase):
         self._send_and_verify_message(
             bot_without_owner,
             stream_name,
-            "Only organization administrators can send to this stream.",
+            "Only organization administrators can send to this channel.",
         )
 
         # Cross realm bots should be allowed
@@ -326,7 +326,7 @@ class MessagePOSTTest(ZulipTestCase):
         guest_profile = self.example_user("polonius")
         # Guests cannot send to non-STREAM_POST_POLICY_EVERYONE streams
         self._send_and_verify_message(
-            guest_profile, stream_name, "Only organization administrators can send to this stream."
+            guest_profile, stream_name, "Only organization administrators can send to this channel."
         )
 
     def test_sending_message_as_stream_post_policy_moderators(self) -> None:
@@ -370,7 +370,7 @@ class MessagePOSTTest(ZulipTestCase):
         self._send_and_verify_message(
             non_admin_profile,
             stream_name,
-            "Only organization administrators and moderators can send to this stream.",
+            "Only organization administrators and moderators can send to this channel.",
         )
         non_admin_owned_bot = self.create_test_bot(
             short_name="whatever3",
@@ -380,7 +380,7 @@ class MessagePOSTTest(ZulipTestCase):
         self._send_and_verify_message(
             non_admin_owned_bot,
             stream_name,
-            "Only organization administrators and moderators can send to this stream.",
+            "Only organization administrators and moderators can send to this channel.",
         )
 
         # Bots without owner (except cross realm bot) cannot send to STREAM_POST_POLICY_MODERATORS streams.
@@ -395,7 +395,7 @@ class MessagePOSTTest(ZulipTestCase):
         self._send_and_verify_message(
             bot_without_owner,
             stream_name,
-            "Only organization administrators and moderators can send to this stream.",
+            "Only organization administrators and moderators can send to this channel.",
         )
 
         # System bots should be allowed
@@ -410,7 +410,7 @@ class MessagePOSTTest(ZulipTestCase):
         self._send_and_verify_message(
             guest_profile,
             stream_name,
-            "Only organization administrators and moderators can send to this stream.",
+            "Only organization administrators and moderators can send to this channel.",
         )
 
     def test_sending_message_as_stream_post_policy_restrict_new_members(self) -> None:
@@ -453,7 +453,7 @@ class MessagePOSTTest(ZulipTestCase):
         # Non admins and their owned bots can send to STREAM_POST_POLICY_RESTRICT_NEW_MEMBERS streams,
         # if the user is not a new member
         self._send_and_verify_message(
-            non_admin_profile, stream_name, "New members cannot send to this stream."
+            non_admin_profile, stream_name, "New members cannot send to this channel."
         )
         non_admin_owned_bot = self.create_test_bot(
             short_name="whatever2",
@@ -461,7 +461,7 @@ class MessagePOSTTest(ZulipTestCase):
             user_profile=non_admin_profile,
         )
         self._send_and_verify_message(
-            non_admin_owned_bot, stream_name, "New members cannot send to this stream."
+            non_admin_owned_bot, stream_name, "New members cannot send to this channel."
         )
 
         non_admin_profile.date_joined = timezone_now() - timedelta(days=11)
@@ -485,7 +485,7 @@ class MessagePOSTTest(ZulipTestCase):
             acting_user=None,
         )
         self._send_and_verify_message(
-            bot_without_owner, stream_name, "New members cannot send to this stream."
+            bot_without_owner, stream_name, "New members cannot send to this channel."
         )
 
         moderator_profile = self.example_user("shiva")
@@ -516,7 +516,7 @@ class MessagePOSTTest(ZulipTestCase):
         guest_profile = self.example_user("polonius")
         # Guests cannot send to non-STREAM_POST_POLICY_EVERYONE streams
         self._send_and_verify_message(
-            guest_profile, stream_name, "Guests cannot send to this stream."
+            guest_profile, stream_name, "Guests cannot send to this channel."
         )
 
     def test_api_message_with_default_to(self) -> None:
@@ -1447,7 +1447,7 @@ class MessagePOSTTest(ZulipTestCase):
 
         # Guest user can't send message to unsubscribed public streams
         result = self.api_post(sender, "/api/v1/messages", payload)
-        self.assert_json_error(result, "Not authorized to send to stream 'public stream'")
+        self.assert_json_error(result, "Not authorized to send to channel 'public stream'")
 
         self.subscribe(sender, stream_name)
         # Guest user can send message to subscribed public streams
diff --git a/zerver/tests/test_message_topics.py b/zerver/tests/test_message_topics.py
index 0d58af24bc..b8c36896e0 100644
--- a/zerver/tests/test_message_topics.py
+++ b/zerver/tests/test_message_topics.py
@@ -160,7 +160,7 @@ class TopicHistoryTest(ZulipTestCase):
         # non-sensible stream id
         endpoint = "/json/users/me/9999999999/topics"
         result = self.client_get(endpoint, {})
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         # out of realm
         bad_stream = self.make_stream(
@@ -169,7 +169,7 @@ class TopicHistoryTest(ZulipTestCase):
         )
         endpoint = f"/json/users/me/{bad_stream.id}/topics"
         result = self.client_get(endpoint, {})
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         # private stream to which I am not subscribed
         private_stream = self.make_stream(
@@ -178,7 +178,7 @@ class TopicHistoryTest(ZulipTestCase):
         )
         endpoint = f"/json/users/me/{private_stream.id}/topics"
         result = self.client_get(endpoint, {})
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_get_topics_web_public_stream_web_public_request(self) -> None:
         iago = self.example_user("iago")
@@ -204,13 +204,13 @@ class TopicHistoryTest(ZulipTestCase):
         stream = get_stream("Verona", self.example_user("iago").realm)
         endpoint = f"/json/users/me/{stream.id}/topics"
         result = self.client_get(endpoint)
-        self.assert_json_error(result, "Invalid stream ID", 400)
+        self.assert_json_error(result, "Invalid channel ID", 400)
 
     def test_get_topics_non_existent_stream_web_public_request(self) -> None:
         non_existent_stream_id = 10000000000000000000000
         endpoint = f"/json/users/me/{non_existent_stream_id}/topics"
         result = self.client_get(endpoint)
-        self.assert_json_error(result, "Invalid stream ID", 400)
+        self.assert_json_error(result, "Invalid channel ID", 400)
 
 
 class TopicDeleteTest(ZulipTestCase):
diff --git a/zerver/tests/test_realm.py b/zerver/tests/test_realm.py
index 8f3e31b594..9300a70689 100644
--- a/zerver/tests/test_realm.py
+++ b/zerver/tests/test_realm.py
@@ -520,7 +520,7 @@ class RealmTest(ZulipTestCase):
             new_stream_announcements_stream_id=orjson.dumps(invalid_notif_stream_id).decode()
         )
         result = self.client_patch("/json/realm", req)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
         realm = get_realm("zulip")
         assert realm.new_stream_announcements_stream is not None
         self.assertNotEqual(realm.new_stream_announcements_stream.id, invalid_notif_stream_id)
@@ -605,7 +605,7 @@ class RealmTest(ZulipTestCase):
             ).decode()
         )
         result = self.client_patch("/json/realm", req)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
         realm = get_realm("zulip")
         assert realm.signup_announcements_stream is not None
         self.assertNotEqual(
@@ -679,7 +679,7 @@ class RealmTest(ZulipTestCase):
             ).decode()
         )
         result = self.client_patch("/json/realm", req)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
         realm = get_realm("zulip")
         assert realm.zulip_update_announcements_stream is not None
         self.assertNotEqual(
diff --git a/zerver/tests/test_subs.py b/zerver/tests/test_subs.py
index fc36a7b775..3a562fc707 100644
--- a/zerver/tests/test_subs.py
+++ b/zerver/tests/test_subs.py
@@ -425,7 +425,7 @@ class TestCreateStreams(ZulipTestCase):
         result = self.api_post(
             user_profile, "/api/v1/users/me/subscriptions", post_data, subdomain="zulip"
         )
-        self.assert_json_error(result, "A default stream cannot be private.")
+        self.assert_json_error(result, "A default channel cannot be private.")
 
     def test_history_public_to_subscribers_zephyr_realm(self) -> None:
         realm = get_realm("zephyr")
@@ -654,7 +654,7 @@ class StreamAdminTest(ZulipTestCase):
         }
         stream_id = get_stream("private_stream_1", user_profile.realm).id
         result = self.client_patch(f"/json/streams/{stream_id}", params)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         stream = self.subscribe(user_profile, "private_stream_1")
         self.assertFalse(stream.is_in_zephyr_realm)
@@ -772,7 +772,7 @@ class StreamAdminTest(ZulipTestCase):
             "is_private": orjson.dumps(True).decode(),
         }
         result = self.client_patch(f"/json/streams/{default_stream.id}", params)
-        self.assert_json_error(result, "A default stream cannot be private.")
+        self.assert_json_error(result, "A default channel cannot be private.")
         self.assertFalse(default_stream.invite_only)
 
         do_change_user_role(user_profile, UserProfile.ROLE_MEMBER, acting_user=None)
@@ -808,7 +808,7 @@ class StreamAdminTest(ZulipTestCase):
         with self.settings(WEB_PUBLIC_STREAMS_ENABLED=False):
             self.assertFalse(user_profile.can_create_web_public_streams())
             self.assertFalse(owner.can_create_web_public_streams())
-            with self.assertRaisesRegex(JsonableError, "Web-public streams are not enabled."):
+            with self.assertRaisesRegex(JsonableError, "Web-public channels are not enabled."):
                 list_to_streams(
                     streams_raw,
                     owner,
@@ -981,7 +981,7 @@ class StreamAdminTest(ZulipTestCase):
         do_change_user_role(user_profile, UserProfile.ROLE_REALM_OWNER, acting_user=None)
         with self.settings(WEB_PUBLIC_STREAMS_ENABLED=False):
             result = self.client_patch(f"/json/streams/{stream_id}", params)
-        self.assert_json_error(result, "Web-public streams are not enabled.")
+        self.assert_json_error(result, "Web-public channels are not enabled.")
 
         bad_params = {
             "is_web_public": orjson.dumps(True).decode(),
@@ -1120,7 +1120,7 @@ class StreamAdminTest(ZulipTestCase):
             "is_private": orjson.dumps(True).decode(),
         }
         result = self.client_patch(f"/json/streams/{stream_id}", params)
-        self.assert_json_error(result, "A default stream cannot be private.")
+        self.assert_json_error(result, "A default channel cannot be private.")
         stream.refresh_from_db()
         self.assertFalse(stream.invite_only)
 
@@ -1142,7 +1142,7 @@ class StreamAdminTest(ZulipTestCase):
             "is_private": orjson.dumps(True).decode(),
         }
         result = self.client_patch(f"/json/streams/{stream_2_id}", bad_params)
-        self.assert_json_error(result, "A default stream cannot be private.")
+        self.assert_json_error(result, "A default channel cannot be private.")
         stream.refresh_from_db()
         self.assertFalse(stream_2.invite_only)
         self.assertFalse(stream_2_id in get_default_stream_ids_for_realm(realm.id))
@@ -1154,7 +1154,7 @@ class StreamAdminTest(ZulipTestCase):
             "is_default_stream": orjson.dumps(True).decode(),
         }
         result = self.client_patch(f"/json/streams/{private_stream_id}", params)
-        self.assert_json_error(result, "A default stream cannot be private.")
+        self.assert_json_error(result, "A default channel cannot be private.")
         self.assertFalse(private_stream_id in get_default_stream_ids_for_realm(realm.id))
 
         params = {
@@ -1472,14 +1472,14 @@ class StreamAdminTest(ZulipTestCase):
 
     def test_unarchive_stream_active_stream(self) -> None:
         stream = self.make_stream("new_stream")
-        with self.assertRaisesRegex(JsonableError, "Stream is not currently deactivated"):
+        with self.assertRaisesRegex(JsonableError, "Channel is not currently deactivated"):
             do_unarchive_stream(stream, new_name="new_stream", acting_user=None)
 
     def test_unarchive_stream_existing_name(self) -> None:
         stream = self.make_stream("new_stream")
         self.make_stream("existing")
         do_deactivate_stream(stream, acting_user=None)
-        with self.assertRaisesRegex(JsonableError, "Stream named existing already exists"):
+        with self.assertRaisesRegex(JsonableError, "Channel named existing already exists"):
             do_unarchive_stream(stream, new_name="existing", acting_user=None)
 
     def test_unarchive_stream(self) -> None:
@@ -1558,7 +1558,7 @@ class StreamAdminTest(ZulipTestCase):
         do_change_user_role(user_profile, UserProfile.ROLE_REALM_ADMINISTRATOR, acting_user=None)
 
         result = self.client_delete("/json/streams/999999999")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_deactivate_stream_backend_requires_admin(self) -> None:
         user_profile = self.example_user("hamlet")
@@ -1621,11 +1621,11 @@ class StreamAdminTest(ZulipTestCase):
         do_change_user_role(user_profile, UserProfile.ROLE_REALM_ADMINISTRATOR, acting_user=None)
 
         result = self.client_patch(f"/json/streams/{stream.id}", {"new_name": "stream_name1"})
-        self.assert_json_error(result, "Stream already has that name!")
+        self.assert_json_error(result, "Channel already has that name.")
         result = self.client_patch(f"/json/streams/{stream.id}", {"new_name": "Denmark"})
-        self.assert_json_error(result, "Stream name 'Denmark' is already taken.")
+        self.assert_json_error(result, "Channel name already in use.")
         result = self.client_patch(f"/json/streams/{stream.id}", {"new_name": "denmark "})
-        self.assert_json_error(result, "Stream name 'denmark' is already taken.")
+        self.assert_json_error(result, "Channel name already in use.")
 
         # Do a rename that is case-only--this should succeed.
         result = self.client_patch(f"/json/streams/{stream.id}", {"new_name": "sTREAm_name1"})
@@ -1784,7 +1784,7 @@ class StreamAdminTest(ZulipTestCase):
                 "is_private": orjson.dumps(True).decode(),
             },
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_non_admin_cannot_access_unsub_private_stream(self) -> None:
         iago = self.example_user("iago")
@@ -1802,13 +1802,13 @@ class StreamAdminTest(ZulipTestCase):
         stream_id = get_stream("private_stream_1", hamlet.realm).id
 
         result = self.client_patch(f"/json/streams/{stream_id}", {"new_name": "private_stream_2"})
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         result = self.client_patch(
             f"/json/streams/{stream_id}",
             {"description": "new description"},
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         result = self.client_patch(
             f"/json/streams/{stream_id}",
@@ -1816,10 +1816,10 @@ class StreamAdminTest(ZulipTestCase):
                 "is_private": orjson.dumps(True).decode(),
             },
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         result = self.client_delete(f"/json/streams/{stream_id}")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_change_stream_description(self) -> None:
         user_profile = self.example_user("iago")
@@ -2332,7 +2332,7 @@ class StreamAdminTest(ZulipTestCase):
             f"/json/streams/{stream.id}",
             {"can_remove_subscribers_group": orjson.dumps(moderators_system_group.id).decode()},
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         self.subscribe(user_profile, "stream_name2")
         result = self.client_patch(
@@ -2489,12 +2489,12 @@ class StreamAdminTest(ZulipTestCase):
             "/json/users/me/subscriptions",
             {"subscriptions": orjson.dumps([{"name": deactivated_stream_name}]).decode()},
         )
-        self.assert_json_error(result, f"Unable to access stream ({deactivated_stream_name}).")
+        self.assert_json_error(result, f"Unable to access channel ({deactivated_stream_name}).")
 
         # You cannot re-archive the stream
         with self.capture_send_event_calls(expected_num_events=0) as events:
             result = self.client_delete("/json/streams/" + str(stream_id))
-        self.assert_json_error(result, "Stream is already deactivated")
+        self.assert_json_error(result, "Channel is already deactivated")
 
     def test_you_must_be_realm_admin(self) -> None:
         """
@@ -2507,13 +2507,13 @@ class StreamAdminTest(ZulipTestCase):
         stream = self.make_stream("other_realm_stream", realm=other_realm)
 
         result = self.client_delete("/json/streams/" + str(stream.id))
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         # Even becoming a realm admin doesn't help us for an out-of-realm
         # stream.
         do_change_user_role(user_profile, UserProfile.ROLE_REALM_ADMINISTRATOR, acting_user=None)
         result = self.client_delete("/json/streams/" + str(stream.id))
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_delete_public_stream(self) -> None:
         """
@@ -2964,12 +2964,12 @@ class DefaultStreamTest(ZulipTestCase):
         stream = self.make_stream(stream_name, invite_only=True)
         self.subscribe(self.example_user("iago"), stream_name)
         result = self.client_post("/json/default_streams", dict(stream_id=stream.id))
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         # Test admin can't add subscribed private stream also.
         self.subscribe(user_profile, stream_name)
         result = self.client_post("/json/default_streams", dict(stream_id=stream.id))
-        self.assert_json_error(result, "Private streams cannot be made default.")
+        self.assert_json_error(result, "Private channels cannot be made default.")
 
     def test_guest_user_access_to_streams(self) -> None:
         user_profile = self.example_user("polonius")
@@ -3145,7 +3145,7 @@ class DefaultStreamGroupTest(ZulipTestCase):
             "/json/default_stream_groups/12345/streams",
             {"op": "add", "stream_names": orjson.dumps(new_stream_names).decode()},
         )
-        self.assert_json_error(result, "Default stream group with id '12345' does not exist.")
+        self.assert_json_error(result, "Default channel group with id '12345' does not exist.")
 
         result = self.client_patch(f"/json/default_stream_groups/{group_id}/streams", {"op": "add"})
         self.assert_json_error(result, "Missing 'stream_names' argument")
@@ -3183,13 +3183,13 @@ class DefaultStreamGroupTest(ZulipTestCase):
             "/json/default_stream_groups/12345/streams",
             {"op": "remove", "stream_names": orjson.dumps(new_stream_names).decode()},
         )
-        self.assert_json_error(result, "Default stream group with id '12345' does not exist.")
+        self.assert_json_error(result, "Default channel group with id '12345' does not exist.")
 
         result = self.client_patch(
             f"/json/default_stream_groups/{group_id}/streams",
             {"op": "remove", "stream_names": orjson.dumps(["random stream name"]).decode()},
         )
-        self.assert_json_error(result, "Invalid stream name 'random stream name'")
+        self.assert_json_error(result, "Invalid channel name 'random stream name'")
 
         streams.remove(new_streams[0])
         result = self.client_patch(
@@ -3220,7 +3220,7 @@ class DefaultStreamGroupTest(ZulipTestCase):
             "/json/default_stream_groups/12345",
             {"new_description": new_description},
         )
-        self.assert_json_error(result, "Default stream group with id '12345' does not exist.")
+        self.assert_json_error(result, "Default channel group with id '12345' does not exist.")
 
         result = self.client_patch(
             f"/json/default_stream_groups/{group_id}",
@@ -3266,7 +3266,9 @@ class DefaultStreamGroupTest(ZulipTestCase):
         self.assert_length(default_stream_groups, 0)
 
         result = self.client_delete(f"/json/default_stream_groups/{group_id}")
-        self.assert_json_error(result, f"Default stream group with id '{group_id}' does not exist.")
+        self.assert_json_error(
+            result, f"Default channel group with id '{group_id}' does not exist."
+        )
 
     def test_invalid_default_stream_group_name(self) -> None:
         self.login("iago")
@@ -3420,7 +3422,7 @@ class SubscriptionPropertiesTest(ZulipTestCase):
             },
         )
         self.assert_json_error(
-            result, "Not subscribed to stream id {}".format(not_subbed[0]["stream_id"])
+            result, "Not subscribed to channel ID {}".format(not_subbed[0]["stream_id"])
         )
 
     def test_set_color_missing_color(self) -> None:
@@ -3720,7 +3722,7 @@ class SubscriptionPropertiesTest(ZulipTestCase):
                 ).decode()
             },
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_set_invalid_property(self) -> None:
         """
@@ -3858,7 +3860,7 @@ class SubscriptionRestApiTest(ZulipTestCase):
             "/api/v1/users/me/subscriptions/121",
             {"property": "is_muted", "value": "somevalue"},
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_bad_add_parameters(self) -> None:
         user = self.example_user("hamlet")
@@ -5081,7 +5083,7 @@ class SubscriptionAPITest(ZulipTestCase):
         )
         self.assert_json_error(
             result,
-            "You can only invite other Zephyr mirroring users to private streams.",
+            "You can only invite other Zephyr mirroring users to private channels.",
             status_code=400,
         )
 
@@ -5304,7 +5306,7 @@ class SubscriptionAPITest(ZulipTestCase):
             "/json/users/me/subscriptions",
             {"subscriptions": orjson.dumps(streams_to_remove).decode()},
         )
-        self.assert_json_error(result, f"Stream(s) ({random_streams[0]}) do not exist")
+        self.assert_json_error(result, f"Channel(s) ({random_streams[0]}) do not exist")
 
     def get_subscription(self, user_profile: UserProfile, stream_name: str) -> Subscription:
         stream = get_stream(stream_name, self.test_realm)
@@ -5675,14 +5677,14 @@ class GetStreamsTest(ZulipTestCase):
         self.assertEqual(json["stream"]["stream_id"], denmark_stream.id)
 
         result = self.client_get("/json/streams/9999")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         private_stream = self.make_stream("private_stream", invite_only=True)
         self.subscribe(self.example_user("cordelia"), "private_stream")
 
         # Non-admins cannot access unsubscribed private streams.
         result = self.client_get(f"/json/streams/{private_stream.id}")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         self.login("iago")
         result = self.client_get(f"/json/streams/{private_stream.id}")
@@ -5712,7 +5714,7 @@ class GetStreamsTest(ZulipTestCase):
 
         self.login("polonius")
         result = self.client_get(f"/json/streams/{denmark_stream.id}/email_address")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         self.subscribe(polonius, "Denmark")
         result = self.client_get(f"/json/streams/{denmark_stream.id}/email_address")
@@ -5733,7 +5735,7 @@ class GetStreamsTest(ZulipTestCase):
 
         self.unsubscribe(hamlet, "Denmark")
         result = self.client_get(f"/json/streams/{denmark_stream.id}/email_address")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         self.login("iago")
         result = self.client_get(f"/json/streams/{denmark_stream.id}/email_address")
@@ -5742,7 +5744,7 @@ class GetStreamsTest(ZulipTestCase):
 
         self.unsubscribe(iago, "Denmark")
         result = self.client_get(f"/json/streams/{denmark_stream.id}/email_address")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
 
 class StreamIdTest(ZulipTestCase):
@@ -5758,7 +5760,7 @@ class StreamIdTest(ZulipTestCase):
         user = self.example_user("hamlet")
         self.login_user(user)
         result = self.client_get("/json/get_stream_id", {"stream": "wrongname"})
-        self.assert_json_error(result, "Invalid stream name 'wrongname'")
+        self.assert_json_error(result, "Invalid channel name 'wrongname'")
 
 
 class InviteOnlyStreamTest(ZulipTestCase):
@@ -5816,7 +5818,7 @@ class InviteOnlyStreamTest(ZulipTestCase):
         # Subscribing oneself to an invite-only stream is not allowed
         self.login_user(othello)
         result = self.common_subscribe_to_streams(othello, [stream_name], allow_fail=True)
-        self.assert_json_error(result, "Unable to access stream (Saxony).")
+        self.assert_json_error(result, "Unable to access channel (Saxony).")
 
         # authorization_errors_fatal=False works
         self.login_user(othello)
@@ -6334,7 +6336,7 @@ class GetSubscribersTest(ZulipTestCase):
         # Verify another user can't get the data.
         self.login("cordelia")
         result = self.client_get(f"/json/streams/{stream_id}/members")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         # But an organization administrator can
         self.login("iago")
@@ -6347,7 +6349,7 @@ class GetSubscribersTest(ZulipTestCase):
         """
         stream_id = 99999999
         result = self.client_get(f"/json/streams/{stream_id}/members")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_json_get_subscribers(self) -> None:
         """
@@ -6402,7 +6404,7 @@ class GetSubscribersTest(ZulipTestCase):
         # Try to fetch the subscriber list as a non-member & non-realm-admin-user.
         stream_id = get_stream(stream_name, user_profile.realm).id
         result = self.make_subscriber_request(stream_id, user=user_profile)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         # Try to fetch the subscriber list as a non-member & realm-admin-user.
         self.login("iago")
@@ -6425,9 +6427,9 @@ class AccessStreamTest(ZulipTestCase):
         othello = self.example_user("othello")
 
         # Nobody can access a stream that doesn't exist
-        with self.assertRaisesRegex(JsonableError, "Invalid stream ID"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel ID"):
             access_stream_by_id(hamlet, 501232)
-        with self.assertRaisesRegex(JsonableError, "Invalid stream name 'invalid stream'"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel name 'invalid stream'"):
             access_stream_by_name(hamlet, "invalid stream")
 
         # Hamlet can access the private stream
@@ -6440,9 +6442,9 @@ class AccessStreamTest(ZulipTestCase):
         self.assertEqual(sub_ret, sub_ret2)
 
         # Othello cannot access the private stream
-        with self.assertRaisesRegex(JsonableError, "Invalid stream ID"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel ID"):
             access_stream_by_id(othello, stream.id)
-        with self.assertRaisesRegex(JsonableError, "Invalid stream name 'new_private_stream'"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel name 'new_private_stream'"):
             access_stream_by_name(othello, stream.name)
 
         # Both Othello and Hamlet can access a public stream that only
@@ -6459,19 +6461,19 @@ class AccessStreamTest(ZulipTestCase):
         mit_realm = get_realm("zephyr")
         mit_stream = ensure_stream(mit_realm, "mit_stream", invite_only=False, acting_user=None)
         sipbtest = self.mit_user("sipbtest")
-        with self.assertRaisesRegex(JsonableError, "Invalid stream ID"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel ID"):
             access_stream_by_id(hamlet, mit_stream.id)
-        with self.assertRaisesRegex(JsonableError, "Invalid stream name 'mit_stream'"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel name 'mit_stream'"):
             access_stream_by_name(hamlet, mit_stream.name)
-        with self.assertRaisesRegex(JsonableError, "Invalid stream ID"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel ID"):
             access_stream_by_id(sipbtest, stream.id)
-        with self.assertRaisesRegex(JsonableError, "Invalid stream name 'new_private_stream'"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel name 'new_private_stream'"):
             access_stream_by_name(sipbtest, stream.name)
 
         # MIT realm users cannot access even public streams in their realm
-        with self.assertRaisesRegex(JsonableError, "Invalid stream ID"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel ID"):
             access_stream_by_id(sipbtest, mit_stream.id)
-        with self.assertRaisesRegex(JsonableError, "Invalid stream name 'mit_stream'"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel name 'mit_stream'"):
             access_stream_by_name(sipbtest, mit_stream.name)
 
         # But they can access streams they are subscribed to
@@ -6486,7 +6488,7 @@ class AccessStreamTest(ZulipTestCase):
         stream = self.make_stream(stream_name, guest_user_profile.realm, invite_only=False)
 
         # Guest user don't have access to unsubscribed public streams
-        with self.assertRaisesRegex(JsonableError, "Invalid stream ID"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel ID"):
             access_stream_by_id(guest_user_profile, stream.id)
 
         # Guest user have access to subscribed public streams
@@ -6499,7 +6501,7 @@ class AccessStreamTest(ZulipTestCase):
         stream_name = "private_stream_1"
         stream = self.make_stream(stream_name, guest_user_profile.realm, invite_only=True)
         # Obviously, a guest user doesn't have access to unsubscribed private streams either
-        with self.assertRaisesRegex(JsonableError, "Invalid stream ID"):
+        with self.assertRaisesRegex(JsonableError, "Invalid channel ID"):
             access_stream_by_id(guest_user_profile, stream.id)
 
         # Guest user have access to subscribed private streams
diff --git a/zerver/tests/test_typing.py b/zerver/tests/test_typing.py
index 21d0021cd4..9e94e226c7 100644
--- a/zerver/tests/test_typing.py
+++ b/zerver/tests/test_typing.py
@@ -145,7 +145,7 @@ class TypingValidateStreamIdTopicArgumentsTest(ZulipTestCase):
                 "topic": topic_name,
             },
         )
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
 
 class TypingHappyPathTestDirectMessages(ZulipTestCase):
diff --git a/zerver/tests/test_user_topics.py b/zerver/tests/test_user_topics.py
index bf5ab4c697..08f3144f42 100644
--- a/zerver/tests/test_user_topics.py
+++ b/zerver/tests/test_user_topics.py
@@ -190,15 +190,15 @@ class MutedTopicsTestsDeprecated(ZulipTestCase):
 
         data = {"stream_id": 999999999, "topic": "Verona3", "op": "add"}
         result = self.api_patch(user, url, data)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         data = {"topic": "Verona3", "op": "add"}
         result = self.api_patch(user, url, data)
-        self.assert_json_error(result, "Please supply 'stream'.")
+        self.assert_json_error(result, "Missing 'stream_id' argument")
 
         data = {"stream": stream.name, "stream_id": stream.id, "topic": "Verona3", "op": "add"}
         result = self.api_patch(user, url, data)
-        self.assert_json_error(result, "Please choose one: 'stream' or 'stream_id'.")
+        self.assert_json_error(result, "Please supply only one channel parameter: name or ID.")
 
         data = {"stream_id": stream.id, "topic": "a" * (MAX_TOPIC_NAME_LENGTH + 1), "op": "add"}
         result = self.api_patch(user, url, data)
@@ -234,11 +234,11 @@ class MutedTopicsTestsDeprecated(ZulipTestCase):
 
         data = {"topic": "Verona3", "op": "remove"}
         result = self.api_patch(user, url, data)
-        self.assert_json_error(result, "Please supply 'stream'.")
+        self.assert_json_error(result, "Missing 'stream_id' argument")
 
         data = {"stream": stream.name, "stream_id": stream.id, "topic": "Verona3", "op": "remove"}
         result = self.api_patch(user, url, data)
-        self.assert_json_error(result, "Please choose one: 'stream' or 'stream_id'.")
+        self.assert_json_error(result, "Please supply only one channel parameter: name or ID.")
 
         data = {"stream_id": stream.id, "topic": "a" * (MAX_TOPIC_NAME_LENGTH + 1), "op": "remove"}
         result = self.api_patch(user, url, data)
@@ -447,7 +447,7 @@ class MutedTopicsTests(ZulipTestCase):
             "visibility_policy": UserTopic.VisibilityPolicy.MUTED,
         }
         result = self.api_post(user, url, data)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         stream = get_stream("Verona", user.realm)
         data = {
@@ -472,7 +472,7 @@ class MutedTopicsTests(ZulipTestCase):
         }
 
         result = self.api_post(user, url, data)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         stream = get_stream("Verona", user.realm)
         data = {
@@ -663,7 +663,7 @@ class UnmutedTopicsTests(ZulipTestCase):
         }
 
         result = self.api_post(user, url, data)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
     def test_unmuted_topic_remove_invalid(self) -> None:
         user = self.example_user("hamlet")
@@ -677,7 +677,7 @@ class UnmutedTopicsTests(ZulipTestCase):
         }
 
         result = self.api_post(user, url, data)
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
 
 class AutomaticallyFollowTopicsTests(ZulipTestCase):
diff --git a/zerver/tests/test_users.py b/zerver/tests/test_users.py
index ac29064afb..def5bca463 100644
--- a/zerver/tests/test_users.py
+++ b/zerver/tests/test_users.py
@@ -1492,7 +1492,7 @@ class UserProfileTest(ZulipTestCase):
 
         # Invalid stream ID.
         result = self.client_get(f"/json/users/{iago.id}/subscriptions/25")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         result = orjson.loads(
             self.client_get(f"/json/users/{iago.id}/subscriptions/{stream.id}").content
@@ -1541,7 +1541,7 @@ class UserProfileTest(ZulipTestCase):
         # Unsubscribed non-admins cannot check subscription status in a private stream.
         self.login("shiva")
         result = self.client_get(f"/json/users/{iago.id}/subscriptions/{stream.id}")
-        self.assert_json_error(result, "Invalid stream ID")
+        self.assert_json_error(result, "Invalid channel ID")
 
         # Subscribed non-admins can check subscription status in a private stream
         self.subscribe(self.example_user("shiva"), stream.name)
diff --git a/zerver/views/streams.py b/zerver/views/streams.py
index 3db4590e94..b45ac7583c 100644
--- a/zerver/views/streams.py
+++ b/zerver/views/streams.py
@@ -130,7 +130,7 @@ def add_default_stream(
 ) -> HttpResponse:
     (stream, sub) = access_stream_by_id(user_profile, stream_id)
     if stream.invite_only:
-        raise JsonableError(_("Private streams cannot be made default."))
+        raise JsonableError(_("Private channels cannot be made default."))
     do_add_default_stream(stream)
     return json_success(request)
 
@@ -296,7 +296,7 @@ def update_stream_backend(
 
     # Ensure that a stream cannot be both a default stream for new users and private
     if proposed_is_private and proposed_is_default_stream:
-        raise JsonableError(_("A default stream cannot be private."))
+        raise JsonableError(_("A default channel cannot be private."))
 
     if is_private is not None:
         # We require even realm administrators to be actually
@@ -309,7 +309,7 @@ def update_stream_backend(
     # web-public, we don't use an "is not None" check.
     if is_web_public:
         if not user_profile.realm.web_public_streams_enabled():
-            raise JsonableError(_("Web-public streams are not enabled."))
+            raise JsonableError(_("Web-public channels are not enabled."))
         if not user_profile.can_create_web_public_streams():
             raise JsonableError(_("Insufficient permission"))
 
@@ -351,7 +351,7 @@ def update_stream_backend(
     if new_name is not None:
         new_name = new_name.strip()
         if stream.name == new_name:
-            raise JsonableError(_("Stream already has that name!"))
+            raise JsonableError(_("Channel already has that name."))
         if stream.name.lower() != new_name.lower():
             # Check that the stream name is available (unless we are
             # are only changing the casing of the stream name).
@@ -380,7 +380,7 @@ def update_stream_backend(
         ] != getattr(stream, setting_group_id_name):
             if sub is None and stream.invite_only:
                 # Admins cannot change this setting for unsubscribed private streams.
-                raise JsonableError(_("Invalid stream ID"))
+                raise JsonableError(_("Invalid channel ID"))
 
             user_group_id = request_settings_dict[setting_group_id_name]
             user_group = access_user_group_for_setting(
@@ -636,7 +636,7 @@ def add_subscriptions_backend(
     )
     if len(unauthorized_streams) > 0 and authorization_errors_fatal:
         raise JsonableError(
-            _("Unable to access stream ({channel_name}).").format(
+            _("Unable to access channel ({channel_name}).").format(
                 channel_name=unauthorized_streams[0].name,
             )
         )
@@ -649,7 +649,7 @@ def add_subscriptions_backend(
         and not all(stream.invite_only for stream in streams)
     ):
         raise JsonableError(
-            _("You can only invite other Zephyr mirroring users to private streams.")
+            _("You can only invite other Zephyr mirroring users to private channels.")
         )
 
     if is_default_stream:
@@ -1016,7 +1016,7 @@ def update_subscription_properties_backend(
         (stream, sub) = access_stream_by_id(user_profile, stream_id)
         if sub is None:
             raise JsonableError(
-                _("Not subscribed to stream id {channel_id}").format(channel_id=stream_id)
+                _("Not subscribed to channel ID {channel_id}").format(channel_id=stream_id)
             )
 
         try:
diff --git a/zerver/views/user_topics.py b/zerver/views/user_topics.py
index 43d68d38f8..4b39dd45a5 100644
--- a/zerver/views/user_topics.py
+++ b/zerver/views/user_topics.py
@@ -99,7 +99,7 @@ def update_user_topic(
     visibility_policy: int = REQ(json_validator=check_int_in(UserTopic.VisibilityPolicy.values)),
 ) -> HttpResponse:
     if visibility_policy == UserTopic.VisibilityPolicy.INHERIT:
-        error = _("Invalid stream ID")
+        error = _("Invalid channel ID")
         stream = access_stream_to_remove_visibility_policy_by_id(user_profile, stream_id, error)
     else:
         (stream, sub) = access_stream_by_id(user_profile, stream_id)