Hello Nina,
A dialcet* is a form of a language spoken in a particular geographical area or by members of a particular social class or occupational group, distinguished by its vocabulary, grammar, and pronunciation.
It could also refer to an inferior form of language.
It is kind of an accent, lingo ,jargon or localism.
Slang* consists of words, expressions, and meanings that are informal and are used by people who know each other very well or who have the same interests.It includes mostly expressions that are not considered appropriate for formal occasions; often vituperative ( marked by harsh abusive criticism ) or vulgar.