Add documentation on translating Zulip.

README.md

@@ -62,6 +62,11 @@ any security issues you discover to support@zulip.com.
 app; the [desktop][], [Android][], and [iOS][] apps are separate
 repositories.
 
+* **Translations**.  Zulip is in the process of being translated into
+10+ languages, and we love contributions to our translations.  See our
+[translating documentation](transifex) if you're interested in
+contributing!
+
 [cla]: https://opensource.dropbox.com/cla/
 [doc]: https://zulip.readthedocs.org/
 [doc-commit-style]: http://zulip.readthedocs.org/en/latest/code-style.html#commit-messages
@@ -73,6 +78,7 @@ repositories.
 [desktop]: https://github.com/zulip/zulip-desktop
 [android]: https://github.com/zulip/zulip-android
 [ios]: https://github.com/zulip/zulip-ios
+[transifex]: https://www.transifex.com/zulip/zulip/
 
 How to get involved with contributing to Zulip
 ==============================================

docs/index.rst

@@ -21,6 +21,7 @@ Contents:
    schema-migrations
    front-end-build-process
    mypy
+   translating
    roadmap
 
 Indices and tables

docs/translating.md

@@ -0,0 +1,19 @@
+# Translating Zulip
+
+Zulip has full support for unicode, so you can already use your
+preferred language everywhere in Zulip.
+
+To make Zulip even better for users around the world, the Zulip UI is
+being translated into a number of major languages, including Spanish,
+German, French, Chinese, Russian, and Japanese, with varying levels of
+progress.  If you speak a language other than English, your help with
+translating Zulip would be greatly appreciated!
+
+If you're interested in contributing translations to Zulip, join the
+[Zulip project on Transifex](https://www.transifex.com/zulip/zulip/)
+and ask to join any languages you'd like to contribute to (or add new
+ones).  Transifex's notification system sometimes fails to notify the
+maintainers when you ask to join a project, so please send a quick
+email to zulip-core@googlegroups.com when you request to join the
+project or add a language so that we can be sure to accept your
+request to contribute.