Japanese has no gendered third person pronouns or adjectives (edit: i mean grammatically gendered, I can't think of anything now but there also might be adjectives you use exclusively for men/women...) etc. and you can also talk about someone without confirming their sex. But there are different "I"s depending on whether you are male or female. Now, obviously anyone can use whichever they like, but nobody will actually think a woman is a man just because she uses the masculine "I". People will probably think she is a weirdo or a lesbian. Another thing is gendered speech particles, for example ending a sentence in "wa", which is predominantly used by women. Basically that is how people gender themselves, there are other examples, which is how you make yourself sound more girly or more manly.