Loading updated translations needs restarting MuseScore to take effect

Fixed in branch 3.x, commit 31773bd664

_Fix #269740: Retranslate when current language is updated

Previously, when you updated the current language using the Resource Manager, you would only be able to see the updated strings after restarting MuseScore. This was, because the condition to determine whether the current language had been updated was wrong, so the retranslate function would not be called. Now, the condition is correct, and the function is correctly called.
I also renamed some variables to make the code clearer to understand, and I fixed a problem with the variable localeName not being updated on a language switch, which caused that the wrong language appeared at the top of the list in the Resource Manager, and might have caused other problems too._

Automatically closed -- issue fixed for 2 weeks with no activity.