Special-case the language fallback for country-less English

For any other language we need a fallback chain from country-specific to the country-less variants, only for English we don't have a country-less variant but the en_US source code.

Without this "en" translations aren't found and we continue trying other languages before eventually getting to "en_US". This results in unexpected results when using a country-specific variant of English that doesn't have translations and at least one secondary non-English language.

This is unusual though possible on Linux, but common on Android. There language and region can be configured independently (and thus it's easy to get to an English country-specific variant without translations) and multiple languages are common as those not only influence translations but also input handling.