I’m sure you are right. It’s not an area of the code I’ve looked at for a very long time, and not a section I wrote.
However that doesn’t change my answer. Whether it is generated by you or by the code it still results in a Custom Event, and therefore the TYPE entry is defined as free-text so cannot be translatable.
I guess we could restrict such tags to a limited range of TYPEs, but how many, and what ones? Would ten be enough, a hundred, or how many?
It is the same problem with notes, sources, source citations, media titles and many other free-text areas. None of these can ever be translatable by code. It is why my personal site has no language options. Everything is in my language, so I have total control of the display.