Yes, it's in. The word 'adda' in my own native Bengali, has been offcially inducted into the Queen's English. You'll find it listed in the updated Oxford Dictionary.
I love the dynamism of the English language. And I love addas, an untranslatable word meaning, well, you know, groups of like or unlike minded folks in freewheeling intellectual discussions about cabbages and kings. The sort of thing that happpens in writers' groups. I would say even Blogspot, with its galaxy of unique voices, is one gigantic adda.
Other Indian inclusions into English are;
bindaas (Hindi) = carefree
chamcha= toady, flatterer, yes-man
chaddi = underpants
yaar = buddy