Unless I'm missing something, this article only discusses tweets by language, not geography. Many Europeans use English on social media sites given the cosmopolitan nature of Europe and the likelihood that, if there is one language they have in common with friends from other countries in Europe and abroad, it is English.
I'm guessing there's a few lesser spoken European languages in that "all others" category.
Also, those numbers actually suggest that by far the most active language group (relatively speaking) on twitter are the Dutch speakers, who are almost all Europeans. Actually, I thought the number and growth for Dutch had to be a mistake, but other sources [1] do suggest the same trends.
I'm still sceptical about the numbers though, especially German being hardly used seems at odds with older data about twitter usage [2].
Yes and no. No: in France at least, very few people use it. Yes: those who do use it in France, use it to talk people internationally (ie. in English).
I'm guessing there's a few lesser spoken European languages in that "all others" category.