Hi-I'd like some help with Dutch translations

Hello Goldman,

I'm dutch and it would be a pleasure to help with any question you have about the language. What can I do for you?

tough guy - I'd say 'taaie (vent/gozer)' or 'bikkel' (although that does sound slightly old fashioned) or if he is or looks criminally inclined and usually looks heavy, the bear type: 'zware jongen'. This is what you say of bouncers for instance.

tough girl - The first thing that springs to mind is a description instead of a word. I guess people would say 'Een beetje zo'n Lara Croft-achtig wijf' which means more or less 'A bit of a Lara Croft type of girl'.
As for one term... maybe 'stoere meid'.

tomboy - I think 'manwijf' is a good one although it refers to women only, not girls and it's mainly about the appearance, less about the behaviour. You'd suspect a 'manwijf' to be a lesbian. When you do talk about the behaviour, you'd say she's a 'mannelijke vrouw (in gedrag)', or you'd call her 'lomp', as in.. her behaviour is 'lomp'. That is far from a compliment!
A (little) girl who behaves (and usually looks) like a boy is a 'jongensachtig meisje'.

powerfully-built male - kleerkast

powerfully-built female - stevige dame, zwaargebouwde dame. In conversation you usually use gestures or intonation to show that you mean muscular instead of fat. A 'stevige tante' usually refers to a chubby lady.

I hope this will be of help. Good luck with your research. Are you gonna put the results online somewhere?
Cuz I noticed you've been asking questions about loads of languages. It must be an interesting study.

I forgot to answer you slang question.

Jongensachtig meisje isn't slang. It's very normal dutch. It's not obviously offensive, it can be neutral description of a girl. "She's a bit jongensachtig (but there's nothing wrong with that)".

Manwijf could be slang. Hold on, I'll have a look to see what the dictionary says.
It says: "forse en bazige, ruwe vrouw, syn. virago, dragonder, kenau."
So that's the official meaning. It means "sturdy/robust and imperious/domineering, rough woman".
I'd say a woman like that will be found to be manly, but this is not exactly the way in which I and the people around me use this word. Among me and my friends a manwijf is a woman who acts but mainly looks like a man.
Age could have something to do with it. I'm 23. My parents would probably agree with the meaning found in the dictionary.