Como dizer "Largar" em inglês

Could be!

dump something
to put something down in a careless or untidy way
Just dump your stuff over there.
Dump your stuff wherever you want.

Happy New Year!

Also:

Don't (just) leave / drop / throw your stuff on the couch.
Don't (just) leave your stuff lying / sitting on the couch.
Don't (just) leave you stuff lying / sitting around.

"Lie" is always intransitive (never takes an object) whereas "lay" is always transitive (necessarily takes an object). You lay - not lie - objects on a surface, but you leave them to lie - not lay - on said surface.

“Can you stop leaving your stupid crap all over the place?”
“Can you stop leaving things scattered all over the place?/all over the sofa/all over the bedroom?”

(It´s not so gently a way, generally parents do that, but it may or may not work with roomates, coworkers or employees, for example.)

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Other way would be:
Is it unreasonable to ask that sofa be clean and empty, so we have a space left to sit on?
(you are appealling to cleaning to people´s awareness, but not everyone is cleanliness-concious.)

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There are plenty of ways to ask someone to clean after their mess, the better ways is to address the problem, not the person. For instance, it´s more effective to say "no more candy wraps on the sofa, right/for the love of God?" OR in an indirect way "someone forgot some candy wraps on this sofa..." than "You are such a mess!" OR "I can´t believe you are so messy!''

With kids, your children, you can use also a bit of humorous lovely irony, "See, the sofa is so sad today! he is crying because someone left clutter/bags/books/toys all over it!". If the situation persists you can use your authority, what is a bit different with coworkers, roomates, adults, etc.

Good one! well done, Cinnamon!
Happy New Year, as well.

To lie/ fling about (UK)/ around (US)

Stop lying/flinging about your stuff/belongings on the settee.