viisi koiraa on ulkona
Finnish · literally “five dogs is outside” · fully correct
Finnish has a quietly bizarre rule: a numeral bigger than one is followed by the partitive singular, and the verb stays third-person singular. So essentially, viisi koiraa on ulkona is, word for word, “five dogs is outside” — and it’s perfectly grammatical.
Internalise that long enough and it stops feeling weird. I quietly created a mental model justifying it in Czech, that it is actually the numeral that is the subject of the sentence, rather than the object - “Five dogs is outside” - Which is exactly the danger: when I hit a Spanish sentence that was ultimately grammatically wrong, it looked like it pulled the same singular-verb move. My Finnish brain nodded it straight through. Spanish has no such rule — a count of things takes plural agreement, full stop: cinco perros están fuera, never está.
Textbook L1/L2 interference — a structure from a language you already own quietly overwriting the one you’re learning. The more languages in the stack, the more cross-traffic, and the more a wrong pattern can feel reassuringly familiar.