help-docs: Update translation general information text.

Adds a shared file with general information about Zulip's
translation project based on the text in web-app's language
picker, and uses that text at the beginning of the help articles
for setting the organization notifications/announcement language
and for the user setting their personal language setting.

Also makes some small edits/updates to the help center article
about the user's personal language setting to align with current
UI and current documentation styles.

templates/zerver/help/change-the-default-language-for-your-organization.md

@@ -2,9 +2,7 @@
 
 {!admin-only.md!}
 
-Zulip has been translated or partially translated into dozens of
-languages. You can see which languages Zulip supports, and help add
-support for new languages on **[Transifex](https://www.transifex.com/zulip/zulip/)**.
+{!translation-project-info.md!}
 
 Each user can use Zulip with [their preferred
 language](/help/change-your-language). In addition, if your
@@ -21,13 +19,13 @@ can set the notifications language for the organization. This setting:
   cannot detect their language preferences from their browser,
   including all users [created via the Zulip API][api-create-user].
 
-### Configure the organization notifications language
+## Configure the organization notifications language
 
 {start_tabs}
 
 {settings_tab|organization-settings}
 
-2. Under **Notifications**, change the **Notifications language**.
+1. Under **Notifications**, change the **Notifications language**.
 
 {!save-changes.md!}
 

templates/zerver/help/change-your-language.md

@@ -1,29 +1,29 @@
 # Change your language
 
-Zulip has been translated or partially translated into dozens of
-languages. You can see which languages Zulip supports, and help add
-support for new languages on **[Transifex](https://www.transifex.com/zulip/zulip/)**.
+{!translation-project-info.md!}
 
 If your organization has a primary language other than American
 English, an administrator should also [set the organization
 notifications language][change-org-lang].
 
+!!! warn ""
+
+    **Note**: This setting controls the language of your Zulip UI.
+    It does not alter any message text or topic, or stream name
+    and description.
+
 [change-org-lang]: change-the-default-language-for-your-organization
 
-### Change your language
+## Change your language
 
 {start_tabs}
 
 {settings_tab|display-settings}
 
-2. Under **Language and time**, click the button next to **Language**.
+1. Under **Language and time**, click the button under **Language**.
 
-3. Click on a language.
+1. Select a language.
 
-4. Click **Reload**.
+1. Click **Reload**.
 
 {end_tabs}
-
-!!! tip ""
-
-    You can always send and read messages in any language.

templates/zerver/help/include/translation-project-info.md

@@ -0,0 +1,8 @@
+Zulip has been translated or partially translated into dozens of
+languages by Zulip's amazing community of volunteer translators.
+You can see which languages Zulip supports [on Transifex][transifex-zulip].
+If you'd like to help by contributing as a translator, see the
+[Zulip translation guidelines][translating-zulip] to get started.
+
+[transifex-zulip]: https://www.transifex.com/zulip/zulip/
+[translating-zulip]: https://zulip.readthedocs.io/en/latest/translating/translating.html