If you use Android, it should normally just work with the TTS engine set in android settings.
Unless you don't have one or your engine does not offer either the map language or english.
I am currently working on enabling other TTS languages and notifying the user more noticeably about TTS problems.
Yeah you may need to install another TTS engine, don't know the Graphene TTS situation exactly.
I like SherpaTTS for example.