Translation service: enable language restrictions

This MR introduces manual restriction of available languages.

This is a rather minor issue, but triggers a whole lot of linting -.-

I need this for a fringe case with the banners, and linting this was on my todo anyway, so here we go :)

The changes are very hard to make out since almost everything is marked as changes.

==> Just take a look at the parts where restrictLanguagePool and maxLanguagePool appear (that's just a few), skip the rest it's mostly linting