There is a sizable FLOSS community in spanish-speaking countries, and at Debconf mexico I met some developers spanish-speaking developers who didn't speak english at all. So certainly it's possible, if perhaps not very convinient, to be participate without english skills.
As another anecdote, I was planning to buy a Linux-based STB (dbox2), and turned out the community spoke and documented everything only in german. Eventually I managed to decipher enough from the forums that dbox2 was missing a feature I needed, but it was quite enlightening experience.
With the for example recent translation of kernel docs to Chinese, I presume the trend is only going to continue, creating more and more code and documentation that is not available in english (unless someone translates it first).