I think there is most definitely a place for slang. Properly used, it can lend a vital edge and voice at the appropriate moments when your write. There's nothing wrong with bending the rules, as long as you know what you're doing. Writing would be so boring if writers always followed the rules.
I also sort of resent the idea of there being a "proper" form of a language. Any form with consistent grammar is proper, as far as I'm concerned. I don't ascribe to the idea of dialectic superiority. Every form of a language is unique in its own way, and deserves respect for what it is. There's a difference between being poorly spoken and having a dialect. To relate this to your country, I can think of few things more edgy and poetic than Cockney rhyming slang. It makes me wish I didn't have such a boring Standard American dialect myself.
I agree with all that. But I am not confusing dialectical usage with being poorly spoken. The best writers use regional dialect with expertise, and as you say, it can add both colour and edge to a story. I do however, think it is a mistake to be too regionally dialectical - you can lose part of your audience if your speech is too provincial, and either not understood, or resented.
I mentioned that board where I was nearly thrown out for using terms like 'chick' when I was nearly 15. Well maybe some of those people had good reason to object to my language, because I was trying to talk to those grown-ups like I did with my mates - and I think they resented it. Since then I have been much more careful with my writing.
But yeah Cockney slang can be quite entertaining. See if you can guess the words to which these Cockney expressions allude -
I'm on my Todd
He's in the Daft and Barmy
I'm going to the J.Arthur
Lend us your **** Sparrow, will you?
Don't care for him, he's a bit of a Lester
He's pretty flash since he got his new Jam Jar
Can't stay, I've got a Bottle and Glass in a few minutes
No more of your Porkies please
Careful with that - it cost me a Bobby Moore
She fell down the Apples and Pears
It was a fair way, so I took the Oxo
He was a Tea Leaf
And there's nothing boring about American speech - you wouldn't believe the amount of trouble I got into when I was in your fair land. Like this poor elderly man who was almost apoplectic with frustration when I asked directions to the 'coach station' (Greyhound Bus Depot). I had similar problems with 'the lift' (elevator) and with 'chips' (fries). LOL - I got served what we call 'crisps' when I asked for chips. :lol: