[Feature] Mods Language Filter

[yalov]

Developers introduced many languages, some mod already has user's target language, some hasn't.

I propose:

1. add languages to metadata specification, and show to user at the mod versions panel
2. • introduce language filter (it shows only target language mods) and/or
   • include languages to separate column.
     For example, if user checks target language, then target-language column will appear with [×]/[  ] values (sorting supported). English language mods still is showed. I assume that most users are mostly interested in only one target language.

[HebaruSan]

It might be worth localizing CKAN itself first. A user who prefers a non-English locale for mods might also have difficulty navigating an English-only application, and the same setting could drive both the CKAN display and the mod filter.

[politas]

So far, the only non-English mods we have are translations, and there are only a handful of them. Localizing CKAN sounds like a pretty big task.

[yalov]

There are plenty of not-only-English mods, list at forum has a tendency to become outdated.
https://forum.kerbalspaceprogram.com/index.php?/topic/158018-addon-localization-home/

Introduce it to CKAN makes it up-to-date.

[yalov]

@politas you want "start using the Mod Versions panel to give us extra functionality" at #2154, consider §1 there

[HebaruSan]

• CKAN's GUI was localized in Internationalize the GUI #2749, including a German translation.
• We've been collecting the locales of modules in metadata since Extract locales from downloads #2760.
• Master Search box #2736 would provide a place to put this in the UI.