I can share the general process that I use to create a single SL course with multiple languages. Happy to receive feedback or hear from others on their approach.
1. Create and finalize the English version SL project.
2. Create copies (Save as) of the English version for each language needed.
3. Translate the other language versions using the SL Translate export/import tools.
4. Create a new SL project which will be the Multilanguage (ML) version of the training.
5. The structure of the ML version should have a single slide/scene where the learner can select a language. the buttons/triggers on the language selector slide should jump to separate scenes that you create for each language.
6. Go into each scene and import the slides from your translated single language SL files.
7. Go back to the language selector slide and create or recheck that the triggers jump to the appropriate first slide of the language scenes.
7. If this is for an LMS and you're tracking completion based on the number of slides, be sure to set the number of slides for completion to the number of slides in just one of the language scenes + 1 for the language selector slide.
Hope this helps.