I lead a Project Management team in the translation industry and work with Articulate Storyline and Rise files very often.
We recommend against building language selection inside the course as seen above with the layering and branching methods. We instead promote Thomas' solution of duplicating the English course and localizing those duplicates. This is optimal for both translation production and long term maintenance.
The major reason is Articulate built a feature to export editable source text as XLIFF, which is the de facto file format for translation. If the course is multilingual then these files are essentially corrupted and cannot be used by modern translation technology. Instead the linguist would have to translate directly on the Articulate course, meaning tools like translation memory, glossary, and QA cannot be leveraged.
I highly recommend to build all source content (not just elearning) with localization in mind. Let the end user select their target language from outside the course, not within.