THE USE OF THE AFFIRMATIVE ‘innit’ is decried by linguists who see it as a barbaric example of ill-educated spoken English. And it’s true that it’s more often used by non-native speakers.
But that’s because English is so complicated. Having to learn the difference between isn’t it, aren’t we, hasn’t she, didn’t they, shouldn’t you. When really, they all perform the same purpose: to affirm what you’ve just said. Innit is short for isn’t it the case. We just don’t have a convenient phrase for it in English.
Other languages have got it right. The French use N’est-ce pas? where the Germans have icht wahr? – and there’s non è vero? in Italian, and ¿no es assi? in Spanish. They all mean innit.