The base game package comes with a Unity Mod called BeppinEx that attempts to contact public internet translation APIs to real-time translate the in-game text.
Given those services are generally from the pre-AI era they don't work very well and give a lot of MTL poetry responses.
You might not be getting any translation at all if you are not allowing internet access from your proton container.
I made a hand translated beppinex cache file (at great personal cost

) so if you grab that and place it in the correct folder it should work without internet access and without shitty MTL. Check the OP for a link.
If that doesn't work, I can't help as I don't know anything about proton.