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Javascript, don't try to learn both at the same time, once you know Javascript, NodeJS will make sense. Learning them at the same time is just going to make it a more complicated process.

CSS is only for web browsers, you don't need that for RageMP unless you're making web pages for CEF. You're right Javascript and NodeJS are the languages, they're pretty similar so understanding Javascript practically will let you understand NodeJS as well. The other languages are C# (currently only serverside) and C++ but by the sounds of it you don't seem to know any languages so I'd stick with Javascript/NodeJS instead of trying to learn more than 2 things.