Hi,
my favourite TTS app is Vocalizer.
One of its features is the user's dictionary (actually a separate one for each installed language) which enables you to change the pronunciations you think are incorrect.
This feature works with every app I have that uses TTS - except for Navigator; it completely ignores my entries, and the half a dozen mispronounced foreign language street names I have so far encountered keep being mispronounced, whereas the same names, read aloud by an eBook reader, sound just like I want them to sound.
Is there anything that can be done about this?
[...and no, Google is not an alternative, because I like the three voices I use (German, French, Irish English) MUCH better than any other voice I have found on the Android platform.]