My anecdotal example: Italian living in Catalonia (for a few years now, but moved as an adult), I speak both Catalan and Spanish with no Italian accent and what

My anecdotal example: Italian living in Catalonia (for a few years now, but moved as an adult), I speak both Catalan and Spanish with no Italian accent and what's even "worse", I speak Italian with Spanish accent ^^; I know these languages are all very similar, so that helped a lot for sure, but the 12 years rule is definitely not absolute.