For English-language words. I’ve always been at a loss for how to figure out what the slang term for something is (or if there even is one) in another language. ML translation apps seemingly never output slang.
I know Spanish and Portuguese have AsiHablamos[1] and Dicionário inFormal[2], respectively. I'd love to know if any other languages have their own slang dictionaries.
Wiktionary (both the English and the correct language version) can be helpful.
For "culturally accepted" slang, yes — the kind that you'd actually find in a "modern" and unabridged dictionary. Not so much for the kind of passing-fad slang or "cultural niche" slang that you'd generally look to UrbanDictionary for if it were English.