Fix locale and language-dependent code in the product

[rzhao271]

The language pack recommender, especially on Windows, relies on the app.getPreferredSystemLanguages() API in order to properly recommend language packs.

The usage of that API has been temporarily reverted to fix the regression #166936. The revert should also incidentally fix #168583 and #167871.

This issue looks into using that API again and the processing needed on the output to ensure that the results do not break any areas outside of the language recommender.

TODO

• Determine which users of platform.locale actually require the system locale, and which ones merely require the language variable.
• Determine how the language variable is actually set. platform.locale is set either through app.getLocale() or app.getPreferredSystemLanguages()[0].
• Modify the code as needed

[rzhao271]

Ironically, many parts of the program want to use the application language instead of the system locale.
The language recommender system seems to be the only part of the application that requires the list of system languages, which is what the original Electron API change in main.js helped with.

[TylerLeonhardt]

Determine how the language variable is actually set. platform.locale is set either through app.getLocale() or app.getPreferredSystemLanguages()[0].

language is set when you install a language pack or it's set to en by default.