Add user documentation for translation and localization

docs/source/index.rst

@@ -44,6 +44,7 @@ JupyterLab is the next-generation web-based user interface for Project Jupyter.
    user/extensions
    user/jupyterhub
    user/export
+   user/language
 
 .. toctree::
    :maxdepth: 1

docs/source/user/language.rst

@@ -0,0 +1,61 @@
+.. _language:
+
+Localization and language
+-------------------------
+
+Staring with version 3.0, JupyterLab provides the ability to set
+the display language of the user interface.
+
+Language packs
+~~~~~~~~~~~~~~
+
+To be able to provide a new display language, you will need to 
+install a language pack.
+
+Visit the `language packs repository <https://github.com/jupyterlab/language-packs/>`__
+for a list of available packs.
+
+Installing
+''''''''''
+
+Language packs are identified by the four letter code of the language and
+variante they provide. For example, for Simplified Chinese the language
+pack code is ``zh-CN`` and you can install it with ``conda`` or ``pip``.
+
+If you use conda with conda-forge packages:
+
+.. code:: bash
+
+   conda install -c conda-forge jupyterlab-language-pack-zh-CN
+
+If you use Pip:
+
+.. code:: bash
+
+   pip install jupyterlab-language-pack-zh-CN
+
+Changing the display language
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To change the interface language, select the Settings menu and then
+select the desired language in the Language submenu.
+
+The Language submenu will inly list any previously installed language
+packs.
+
+.. image:: images/language_settings.png
+   :align: center
+   :class: jp-screenshot
+
+Selecting the new language will prompt for confirmation.
+
+.. image:: images/language_change.png
+   :align: center
+   :class: jp-screenshot
+
+Once you accept, the browser will refresh and the interface will
+now be shown, for this example in Simplified Chinese.
+
+.. image:: images/language_chinese.png
+   :align: center
+   :class: jp-screenshot

tsconfigdoc.json

@@ -230,6 +230,9 @@
     {
       "path": "./packages/statusbar-extension"
     },
+    {
+      "path": "./packages/tabmanager-extension"
+    },
     {
       "path": "./packages/terminal"
     },