I, for one, have studied and become fluent in one European language, and can read another. I prefer to use the word "gender" because it is a neutral word that does not imply any physical act, but refers only to the biological gender.
I find somewhat puzzling the argument that "gender" is merely a grammatical term, like "noun" or "gerund." That argument is rather nonsensical to me, actually. You might as well insist that the words "male" and "female" are merely descriptive of grammatical functions, and have no other meaning than that. But the reality is that the grammatical functions are actually linked to perceptions of the nature of the object being described.
Outside of the grammatical descriptors, languages change over time and across distance. I tend to think that the objection to using "gender" to describe whether a person is male or female is rooted in both time and regional dialect, rather than in any hard-and-fast rule. And I will continue to use the word "gender": I will readily state that my gender is female, but sex is a private matter.
You can think what you want and say what you want but gender is not a sex. That’s some cultural Marxist construction that came out of the humanity departments and it has nothing to do with biology.