I'm Kärt, one of the creators of the French course. We currently have about 4800 words in the French course, and we want to reach 5000 soon. We'd like to expand the course even further, but as we have so much to do, it's not our first priority at the moment.
The English course has about 5100 words, while Russian and Spanish have less, at about 3000, but new words are created regularly. The aim is to have at least 5000 words in each course.
You will reach the end of the course once you run out of new words and have mastered all words from your repeat stack.
Bonne continuation !