If the system language is set to one that is not supported by the TTS engine, the TTS toggle cannot be enabled. Unsupported languages in Google TTS include Kazakh, Belarusian, and Persian (I only checked the languages that have translations on Crowdin).
I used the Belarusian for the demonstration: https://photongilbert.s-ul.eu/PJkfrY9c
If it's possible to implement a check for whether the selected language is supported by the TTS engine, I suggest the following solution: when enabling TTS in unsupported languages, automatically enable the "Force language to English" setting so that TTS can still function. Additionally, a pop-up could be displayed: “TTS is not supported for the selected language. English will be used instead.”
If the system language is set to one that is not supported by the TTS engine, the TTS toggle cannot be enabled. Unsupported languages in Google TTS include Kazakh, Belarusian, and Persian (I only checked the languages that have translations on Crowdin).
I used the Belarusian for the demonstration: https://photongilbert.s-ul.eu/PJkfrY9c
If it's possible to implement a check for whether the selected language is supported by the TTS engine, I suggest the following solution: when enabling TTS in unsupported languages, automatically enable the "Force language to English" setting so that TTS can still function. Additionally, a pop-up could be displayed: “TTS is not supported for the selected language. English will be used instead.”