More accurate language depot handling

[NicknineTheEagle]

What problem is this feature trying to solve?

DepotDownloader's handling of language depots is currently not quite accurate as it lacks a few quirks of the actual Steam client.

1. If the app does not support the selected language (it's not listed in "languages" section in app info), Steam falls back to English.
2. If the app does support the selected language but there's no depot for that language, Steam falls back to English depot if one exists (e.g. 12210).
3. Very odd quirk: if English language is selected, English depot exists but the user does not own it and the user owns at least one (or just one?) non-English depot, Steam downloads that non-English depot instead. This is sometimes used to enforce regional content, e.g. 393080 has "Arabic" depot which is actually English with some censored content for Middle Eastern countries.

How would you like it to be solved?

Update DepotDownloader's language depot handling to include these quirks.

Have you considered any alternative solutions

N/A

Additional Information

No response