Create text to speech in different languages but in one training

What is usually done is that language selection is made at the LMS level. So, for example, when I log into my LMS, it signs me into the interface in English. Once logged in, I will see the English courses available to me. No sense in selecting English a second time when I launch a course. I design my classes in my native languages, export all the captions and closed captions, and send them to a localization or translation company to convert them to another language. I can then import the translated text and publish the other language version of the course.

Here is the process captured in a YouTube video: https://youtu.be/MLtttHUHqTE

It's an older video, but the process hasn't changed. 

Bad idea to have multiple languages in the same module. Especially audio clips tend to rather big file sizes, different for each language which makes synching almost impossible. I am not yet talking about the overall file size of the resulting course. Use an individual course for each language, and a main dashboard to navigate to the proper course based on the language choice.

Moreover, did you find sufficient good TTS voices for each language? It is not only the slide audio which needs to be cared for, but maybe also audio clips triggered as object audio or with the Play Audio command. Moreover you'll want to have all labels on buttons, quizzes translated as well. Lot of that can be done by using a dedicated Preferences set and Theme. That is however impossible if you want everything in one course.