What irritates you the most with your own language?
Mine is people who separate words when they write. I'm Norwegian, and we can string together words indefinetly to make a new word. The never ending word may not make any sense, but it is gramatically correct
Still, people write words the wrong way by separating them.
Examples:
"Ananas ringer" means "the pineapple is calling" when written the wrong way. The correct way is "ananasringer" and it means "pineapple rings" (from a tin).
"Prinsesse pult i vinkel" means "a princess fucked at an angle". The correct way to write it is "prinsessepult i vinkel", and it means "an angeled princess desk" (a desk for children, obviously)
"Koke bøker" means "to cook books". The correct way is "kokebøker" and means "cookbooks"
In English, lack of second-person plural, aside from a dozen regionalisms: y'all, yinz, youse, etc.
No distinction between inclusive & exclusive 'we': if I say "we've got to go now", do I expect you to come?
Unnecessarily generated pronouns. I know 'they/them' has been used for individuals for ages, but I still find it awkward. I wish we just used one set of ungendered pronouns for every specific person.