support search with 3-letter language codes or BCP-47

Make it possible to search with 3-letter language IDs (like in mtdata) - integrate the ID conversion tools implemented in mtdata
(https://github.com/thammegowda/mtdata). Even better is to support extensions like script and region as well (BCP-47 with 3-letter codes). Maybe also the original BCP-47 with a mix of 2-letter and 3-letter language codes?