i18n: Add explanation for locales and automatic language setting

[stephanbogner]

As discussed in #9684 I think the docs could be enhanced by adding the following:

• Explanation on locales and language
• A simple example script to set the game’s language based on the player’s OS language

This is my first commit for the docs so I am not sure:

• If the writing style is correct
• If I used the .rst syntax correctly

So help is very much appreciated ❤️

[stephanbogner]

@mhilbrunner and @AThousandShips Thanks for your help ❤️
Should be good now (hopefully)

[stephanbogner]

Ok damn. Will have to get the build tools working locally to be more efficient 😅

[stephanbogner]

@mhilbrunner @AThousandShips

Seems to work now:

Local build output

make FILELIST='tutorials/i18n/internationalizing_games.rst ' html 

sphinx-build -M html -d _build/doctrees   '.'  "_build"/html tutorials/i18n/internationalizing_games.rst 
Sphinx v4.4.0 in Verwendung
Build language: en, i18n tag: False
Lade Übersetzungen [en]…erledigt
loading pickled environment... erledigt
building [mo]: targets for 0 po files that are specified
building [html]: 1 source files given on command line
updating environment: 0 added, 0 changed, 0 removed
looking for now-outdated files... none found
preparing documents... WARNING: search index couldn't be loaded, but not all documents will be built: the index will be incomplete.
erledigt
writing output... [100%] tutorials/i18n/internationalizing_games                                                                                                                     
generating indices... genindex erledigt
writing additional pages... search erledigt
copying images... [100%] tutorials/i18n/img/localized_name.webp                                                                                                                      
copying downloadable files... [100%] tutorials/scripting/gdextension/files/cpp_example/SConstruct                                                                                    
copying static files... erledigt
copying extra files... erledigt
dumping search index in English (code: en)... erledigt
dumping object inventory... erledigt
build abgeschlossen, 1 warning.

The HTML pages are in _build/html.