I can’t recall having done any discussions about the feasibility of multilingual support with BadgeOS, and I can’t imagine it being an easy quick fix either.
The problem is, if I recall right with WPML, is that when that plugin translates posts, it actually creates a new post, I believe in the same post type. Because of the fact that it’s a new post, the original achievement/step/etc associations are broken It’s looking for the achievement with post ID 123, and the translated one has a post ID of 124. Users are having to do the French version to get the French achievement, and the English version to get the English achievement. The two aren’t tied together in the database. I hope this is making sense.
Regarding the last part, I imagine the English Description is getting directly associated with the French achievement as post meta or so, but it’s still going to be for the French achievement, and thus the permalinks would go to the French version.