There have been enough requests for this at this point to implement it.
As per https://github.com/ppy/osu/discussions/27955.
Associate with files and URIs on windows
Localise storage error popup dialog
Localise update-related process strings
Localise remaining strings on import screen of the first-run setup
I have very low hopes translators would be able to correctly navigate this otherwise (especially in languages with different word order).
Display which mods grant pp
Show offset explanation tooltip on settings offset adjust slider bar