Any language is, but not by simple majorities. In practice there is something like a pagerank for people for language usage, just as there is for most topics.

For example, it could be that 99% of people who use the phrase "begs the question" misuse it. But the 1% who don't are not merely a random 1% of the population. So in disputes about how to use the phrase, those who get it wrong tend to defer to those who get it right. You couldn't say the meaning of the phrase had changed till that stopped happening, because it implies by induction that everyone who misuses the phrase would change their usage if called on it.