Not really. The course can be free, but the certification paid. If every year 1% of the user base pays $50 to $100 for certification, that is worth $50M to $100M in revenue. I know there was a time I would pay $100 to get an English certification (before coming to the US for school). I also "help" teach French in college and privately. If they required a certification, I would not have minded paying $200 at that time to get a certificate.