Do you think I will have a chance to work in UK (in a law firm) after a LLM program in UK ?
Or I'll have to return back in my country?

I've noticed that the "job opportunities" threads on this site are often empty. Lots of people talking about what program they're applying to, not so many talking about why they want the LLM.

From what I understand, you'll have a rather hard time getting employment in the UK with only an LLM. You'll do much better returning to your home country after.

Totally agree. I'm in that position. If you want to work in the legal area in the UK you either have to become a solicitor through the Legal Practice Course (LPC, apply early for training contracts!) or in doing the Qualified Lawyers Transfer Test (QLLT, check if and how you're entitled to convert at sra.org.uk). A few law firms have a special "LLM intake" and of course there are the non-legal areas as well. But one should be aware of early deadlines for application.