I’m a swede with fully swedish parents, and I have always lived here, but I’ve always sucked at Swedish, both spelling and vocabulary.
But I’m way better at English, I often use English words because I can’t remember or simply don’t know the Swedish equivalent, and sometimes I just give up and fully use English for whatever I’m trying to explain. I wouldn’t say I’m great at grammar overall, but I’m above average based on how bad most people are.