I just received a request to add a preset for amenity=language_school to my fork of the JOSM presets (that you should be using instead of the original :-)) Nothing to said against that, it is a reasonably popular feature with nearly a 1’000 uses.
Naturally a preset that is essentially just a stub isn’t really helpful, so as always I checked what additional properties should be added, and tagging the taught languages is an obvious attribute that is interesting.
Much to my dismay it seems as if in early 2016 it was infected with the “move values to key” plague. Instead of having two keys, lets say
containing a list of the languages, we now have more than two hundred potential keys for an in principle, simple attribute, making both data consumption, editing and creating a preset more than just difficult (as the keys can have at least three values plus unset, they can’t even be modelled with a checkbox in a preset).
At the time somebody further thought it was a good idea to retag existing language tags to the broken schema: