What are the best English slang dictionaries?

Are you tired of grammar exercises?

Why don’t you dare to learn the more colloquial English that Anglophones around the world use every day?
In the academic world slang (both British and American) has hardly any place; however, students who become familiar with this language will be able to integrate much more easily in the United Kingdom and the United States.
You can learn a lot from a good dictionary.
First of all, you should know that colloquial language hides cultural and historical features. Knowing the slang of English will help you discover all the corners of Anglophone culture.

You can learn “slang” with some of these slang dictionaries

Bilingual Dictionaries English-Spanish ( Harrap’s Slang Dictionary, Bilingual Dictionaries of Slang: Word up!  …),
Traditional slang dictionaries ( A Classical Dictionary of the Vulgar Tongue ,  Urban Dictionary: freshest street slang defined  …),
Commonwealth slang dictionaries ( Western Canadian Dictionary and Phrase-Book, A Popular Dictionary of Australian Slang  …),
American slang dictionaries ( Dictionary of American slang, An American dictionary of slang and colloquial speech  …),
Specialized English slang websites.
Knowing the familiar language is especially useful for trips or stays in the United States, where the colloquial register is very present in everyday life. To learn a foreign language and advance in a few months, nothing better than an intensive study of «slang language» .