Making this ticket at the last minute, since I've already done the work, but: split up the domains into languages, scripts, countries, relationships, instruments, instrument descriptions, statistics, attributes, and everything else goes in the default mb_server domain. This lets us reuse existing lists of translated ISO codes (and lets others use ours), splits out unuseful or not-very-used things (instrument descriptions and statistics), and allows prioritizing much better for translators. Also incidentally fixes some other bugs, but you can read that on the codereview!