Docs: automatically generate the list of locales (#3272)

docs/user-guide/choosing-your-theme.md

@@ -108,20 +108,7 @@ supports the following options:
     The following locales are supported by this theme:
 
     * `en`: English (default)
-    * `de`: German
-    * `es`: Spanish
-    * `fa`: Persian (Farsi)
-    * `fr`: French
-    * `id`: Indonesian
-    * `it`: Italian
-    * `ja`: Japanese
-    * `nb`: Norwegian Bokmål
-    * `nn`: Norwegian Nynorsk
-    * `pt_BR`: Portuguese (Brazil)
-    * `ru`: Russian
-    * `tr`: Turkish
-    * `uk`: Ukrainian
-    * `zh_CN`: Simplified Chinese
+    * (see the list of existing directories `mkdocs/themes/mkdocs/locales/*/`)
 
     See the guide on [localizing your theme] for more information.
 
@@ -198,18 +185,7 @@ theme supports the following options:
     The following locales are supported by this theme:
 
     * `en`: English (default)
-    * `de`: German
-    * `es`: Spanish
-    * `fa`: Persian (Farsi)
-    * `fr`: French
-    * `id`: Indonesian
-    * `it`: Italian
-    * `ja`: Japanese
-    * `pt_BR`: Portuguese (Brazil)
-    * `ru`: Russian
-    * `tr`: Turkish
-    * `uk`: Ukrainian
-    * `zh_CN`: Simplified Chinese
+    * (see the list of existing directories `mkdocs/themes/readthedocs/locales/*/`)
 
     See the guide on [localizing your theme] for more information.
 

docs/user-guide/localizing-your-theme.md

@@ -31,8 +31,8 @@ underscore. For example, some possible locales for English might include `en`,
 For a list of locales supported by the theme you are using, see that theme's
 documentation.
 
-- [mkdocs]
-- [readthedocs]
+- [mkdocs](choosing-your-theme.md#mkdocs-locale)
+- [readthedocs](choosing-your-theme.md#readthedocs-locale)
 
 WARNING:
 If you configure a language locale which is not yet supported by the theme
@@ -58,8 +58,6 @@ If a theme has not yet been translated into your language, feel free to
 contribute a translation using the [Translation Guide].
 
 [Translation Guide]: ../dev-guide/translations.md
-[mkdocs]: choosing-your-theme.md#mkdocs-locale
-[readthedocs]: choosing-your-theme.md#readthedocs-locale
 [locale]: configuration.md#locale
 [theme]: configuration.md#theme
 [ISO-639-1]: https://en.wikipedia.org/wiki/ISO_639-1