I'm not sure, it works for The Witcher 3. Same thing: I have the PS4 version with the Hungarian language support on disc, but when I upgraded from the German Store to the PS5 version, the Hungarian localization was not available, so I upgraded with my "temporary" Hungarian account used for such situations and it worked. (I have been living in Germany for a few years.)
However, I activated the two Witcher 3 expansions (Heart of Stone, Blood & Wine) back then in 2016 in the German Store (physical versions with Gwent decks and download code) and downloaded them from there I'm able to play them in Hungarian, because the game itself was updated from the Hungarian Store to the PS5 version.
It's a complete mess anyway...I have no idea why it should be impossible to choose the language you like.