Linux

Some other quirks I ran into -- native speakers who don't read much often confuse "their", "they're", and "there", because they're homophones. They learn the language as speakers years before they learn to write or cover grammar, and in that environment, it's easy to mentally treat the words as one. The people on that Europe forum virtually never did that.

But one error that did come up -- in languages in Europe, there is often a "Romance" word and a "Germanic" word and they translate directly into each other when you move across languages, whereas in English, sometimes both of the words exist as loanwords and have different meanings. Examples are "manikin" and "mannequin" or "block" and "bloc". I especially saw "block" get used to refer to a political group, whereas normally in English, you'd use "bloc" for that.

One that I'd been aware of for a while that Russians have trouble with is use of the definite and indefinite article. So, in English, you have the definite and indefinite article, "the" and "a". In English, you are required by the language to always indicate whether a thing is a specific thing or an example of a type. I didn't realize until listening to a series of linguistic lectures that that's actually an unusual property for a language to have -- English does that, but most languages do not. In English, you must have "the cat" or "a cat"; you can't just say "cat drank milk". But it was so embedded into my thought process that I hadn't realized that I just always do that. Russian, as well as most languages out there, doesn't work like that.