To really do this you want to break the text to speech into two pieces: use English to turn the text into phonemes, and then use the other language to turn the

To really do this you want to break the text to speech into two pieces: use English to turn the text into phonemes, and then use the other language to turn the phonemes into audio. This only works if your phonemes are encoded pretty generically, though. For example, /f/ in English is labiodental while it's bilabial in Spanish, so if you want your accent changing to work right you'll need to either represent both as /f/ or have a reasonable model for picking the closest sound a speaker of a given language is likely to be able to reproduce for any given input.