just curious. I don't know if writing in different languages yield different rewards. In other words, an article written in French is the same as an article written in English?
English is a universal language so a large percentage of content on the internet is English so just a bigger market for English. French would probably pay the same but it might be harder to find clients/smaller market.
I guess it pretty much depends on the prevalence of authors for each given language. of course you will find a lot more authors willing to write in English or French and a lot less able to write in more exotic languages.