[MU4 Issue] Clicking "Check for language updates" a second time does not always recognise that the language is now up to date

[cbjeukendrup]

To Reproduce Steps to reproduce the behavior:

1. Delete any files from %localappdata%/MuseScore/MuseScore4Development/locale (Windows) or ~/Library/Application Support/MuseScore/MuseScore4Development/locale (macOS).
2. In MuseScore, open Preferences and click "Check for language updates". -> this should download the latest version of the current language.
3. Click that button again -> expected: it will now report that the language is up to date. -> actual: it seems to be downloading and installing the language again.

Originally reported in https://github.com/musescore/MuseScore/issues/15640#issuecomment-1369312401.