Revert "Remove invalid language code "bh" (alias of "bho")"
Still being heavily used for interwiki links.
See eg. https://www.wikidata.org/wiki/Wikidata:Contact_the_development_team#Link_for_bh.wiki
This reverts commit 34a3de0f65609c7ffdaafbf3770001e531a616cf.
Bug: T99059
Change-Id: I6db0c436dc2c7556bbc060584e0a725402238adf