Improve i18n documentation for cog creators (#6595)

docs/framework_i18n.rst

@@ -14,36 +14,96 @@ Basic Usage
 .. code-block:: python
 
     from redbot.core import commands
-    from redbot.core.i18n import Translator, cog_i18n
+    from redbot.core.i18n import Translator, cog_i18n, set_contextual_locales_from_guild
     
+    # The translator should be defined in the module scope, with __file__ as the second parameter
     _ = Translator("ExampleCog", __file__)
 
+    # This decorator must be used for cog and command docstrings to be translated!
     @cog_i18n(_)
-    class ExampleCog:
-        """description"""
+    class ExampleCog(commands.Cog):
+        """Cog description"""
+        def __init__(self, bot):
+            self.bot = bot
 
         @commands.command()
         async def mycom(self, ctx):
-            """command description"""
-            await ctx.send(_("This is a test command"))
+            """Command description"""
+            # Correct way to translate strings:
+            await ctx.send(_("This is a test command run by {author}!").format(author=ctx.author.display_name))
+
+            # !!! Do not do this - String interpolation should happen after translation
+            await ctx.send(_("This is a test command run by {author}!".format(author=ctx.author.display_name)))
+
+            # !!! Do not use f-strings - String interpolation should happen after translation
+            await ctx.send(_(f"This is a test command run by {ctx.author.display_name}!"))
+        
+        @commands.Cog.listener()
+        async def on_message(self, message):
+            # In non-command locations, you must manually call this method for guild locale settings to apply
+            await set_contextual_locales_from_guild(self.bot, message.guild)
+            if message.author.bot:
+                return
+            await message.channel.send(_("This is a non command with translation support!"))
 
 --------
 Tutorial
 --------
 
-After making your cog, generate a :code:`messages.pot` file
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Preparing your cog for translations
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-We recommend using redgettext - a modified version of pygettext for Red.
-You can install redgettext by running :code:`pip install redgettext` in a command prompt.
+The first step to adding translations to your cog is to add Red's internationalization framework
+to the strings in your cog. The first step is to instantiate an instance of
+`redbot.core.i18n.Translator` just after the imports in each file. This object is traditionally 
+stored in the variable ``_`` to reduce its character count and visual impact on the code. Next,
+add the `redbot.core.i18n.cog_i18n` decorator to your cog class. This will allow docstrings of
+the class and its commands to be translated. Every user-facing string that is not a docstring
+should then be wrapped by the Translator object. If variables are included in a string,
+``.format()`` must be used, and should be called after the translation function call. This is
+because ``.format()`` within the translation function call and f-strings cause the interpolation
+to happen **before** the translation is applied. The translation logic needs to match the template
+string to translate it, and will be unable to successfully match after interpolation occurs.
+Finally, any non-command portions of your code, including listeners, tasks, and views, should call
+`redbot.core.i18n.set_contextual_locales_from_guild` prior to translating any strings, as only
+commands are able to implicitly determine which guild's configured locale to use. See the example
+above for the exact recommended syntax.
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Generating a messages.pot file
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+A ``messages.pot`` file is a template for translating all of the strings in your cog. It should
+be generated using ``redgettext`` - a modified version of ``pygettext`` for use with Red cogs.
+You can install ``redgettext`` by running :code:`pip install redgettext` in your development
+environment.
+
+Once you have ``redgettext`` installed, you will now need to run
+
+:code:`python -m redgettext -c [path_to_cog_folder]`
+
+This will generate a ``messages.pot`` file in ``path_to_cog_folder/locales``. This file will
+contain all strings to be translated, including docstrings.
 
-To generate the :code:`messages.pot` file, you will now need to run
-:code:`python -m redgettext -c [path_to_cog]`
-This file will contain all strings to be translated, including
-docstrings.
 (For advanced usage check :code:`python -m redgettext -h`)
 
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Creating language specific translations
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 You can now use a tool like `poedit
-<https://poedit.net/>`_ to translate the strings in your messages.pot file.
+<https://poedit.net/>`_ to translate the strings in your ``messages.pot`` file.
+
+Alternatively, you can use any text editor to manually create translations. To do this, first
+create a copy of the ``messages.pot`` file in the same folder, and name the copy
+``LANGUAGE-CODE.po``, where ``LANGUAGE-CODE`` is a five character language code supported by
+``[p]set locale``. Open the copy in your text editor of choice. This file contains the strings
+in your cog prefixed by ``msgid`` and an empty string for you to apply translations prefixed by
+``msgstr``. The original string should be translated to the target language by modifying the
+associated ``msgstr``. Any variables within curly braces should **not** be translated to avoid
+breaking the code when translations are applied. If keyword arguments were used in ``.format()``
+calls, it may be safe to re-order variables if the grammer of the language requires doing so.
 
 -------------
 API Reference
@@ -51,4 +111,4 @@ API Reference
 
 .. automodule:: redbot.core.i18n
     :members:
-    :special-members: __call__
+    :special-members: __call__, __init__