Hello,
As far as I know Turkish translation for KDE Plasma is far away from the finish. But Turkish translation being incomplete isn't my issue here. If Regional Settings / Formats set to Türkiye, Elisa won't launch at all. If it is changed from Türkiye to Default (C), it will launch but won't play any music. I tested this with neon-user-20201126-1349 and Elisa's both snap and flatpak versions in Discover. Choosing Türkiye/Turkish while installing OS prevents user from Elisa. I have no idea if the issue is either Elisa's or Plasma's translation, formatting, etc.
I'd suggest considering disabling Turkish or Türkiye options from installation until they are complete or fixed

Thanks for all the work. It is amazing

Please file a bug for this on https://bugs.kde.org