Remove language codes from card

[Popolechien]

As mentioned in offspot/imager-service#409

most zims (and configs) are monolingual so the language code on each card appears superfluous (even more so since the zim description would already give an idea of what language is the zim in)

A select box to filter by language already exists, so one can easily sort content.

[kelson42]

I would recommend to do so ONLY if monolingual image.