Starting in Daggerfall Unity 0.15.2, I've embedded AudioSynthesis code and modified string comparisons to be culture and case insensitive.
I reproduced exception in older versions by setting Windows display language to Turkish, then confirmed music MIDI music playing in 0.15.2 with the above changes. Also tested loading a custom SoundFont.
This specific issue with AudioSynthesis and Turkish display language should be resolved now.