Google Assistant is still relatively young, and as such it is constantly being improved and learning new things. It still has missing functionality and little issues, but Google has been working hard on fixing them.
The latest change is the addition of French and Spanish support, though only in the Allo app for the moment. The languages aren’t quite as polished as the already supported ones, but they are functional. Hopefully the languages will soon roll out to Assistant in general, but for now open up the Allo app and check it out!