The Text-to-Speech feature in Final Draft use the text-to-speech function built in the Mac OS or the Microsoft Speech Engine on Windows. We're not aware of other languages unless they're available in a non-U.S. version of the operating system.
If you're on Mac, check the language version of your OS or contact Apple to see if there are other languages available.
On Windows, contact Microsoft to see if there are other versions of their Speech Engine.
Keep in mind that we test the only standard versions of these text-to-speech engines and haven't tested any other versions, if any are available. If they exist and you install foreign-language Text-to-Speech engines they may conflict with the default American English engine. We won't be able to assist you if problems arise from such an installation.