it happened to me several times now, that the installation went OK, but during my 1st routing underway, I keep getting Warning Popups on Android level, that the appropriate TTS engine is not installed. This is nasty, because it re-appears every time the APP wants to make an announcement, which basically makes any NAV impossible. So you have to stop, switch speech off and restart. May be, you could check at installation time, if the proper TTS engine is installed and eventually ask the user to do so, or have it done automatically.
TTS checks are done when is needed, that is when text-to-speech is to be used.
Then if cannot be used, notifies so can install languages, etc. and voice to work.
Hint: can test before drive outside.