In case of technical websites, you have to know English anyway, because even if there is a broken translation of the documentation, function names, enums and all the cool stuff remains in the original language anyway.
You don't, plenty of developers are getting around having to know English as there are other resources for learning.
I think it's a dangerous assumption that everyone knows English. It's especially true in the Spanish-speaking world, where I know developers who can't have a conversation in English but are good enough to be employable.
