I want to spice up some of my bit characters, the folk who only appear for a scene or two and fulfil one purpose. One way of making them more memorable is to have them speak an English dialect, instead of the standard English used by everyone else as well as the narration. It can add humour and also quickly identify them as foreigners or locals.
To be clear, I have no intention to write phonetic dialogue e.g. "Luk at zis 'ere"; I want to adorn the lines with some fresh vocabulary and a grammatical quirk or two.
The setting is a fantasy world so I can pick any dialect I want with no regard for geography. Fictionalising a dialect is also theoretically possible but I highly doubt I'd be any good at it; taking a real-life one is going to be difficult to render accurately. And studying a particular dialect exhaustively seems a great deal of wasted effort for one or two lines of dialogue.
So basically I wonder if there's one or more particularly "easy" dialects to use, that can be used accurately because they are exhaustively described, with a set of grammar rules and a good dictionary.