from you to ya

hi'alllllll
there is some kind of accent in english which converts the word you to ya..is this way of speaking right? wat is it exactly? I mean does it have a name? why some pple say it like that? or its only a sort of slang?

I think it's universal to all accents. It's the way "you" is said in an unstressed syllable when speech is fluid. It's not slang.
e.g. what are ya doing?

Compare this with: what are YOU doing? The "you" here is stressed, so the syllable is sustained for longer and our attention is drawn to the word "you".

that's weird! i once saw one movie when the actor told his lover "I love ya" why didnt he stress the word you as he expresses the greatest feeling in the world?

Because if you stressed "you" then it would be like if your lover was accusing you of cheating.

I don't love Mark, I love YOU, Tom, YOU are the one I love, not Mark.

Generally the stressed word is LOVE.

"Ya" is the weak form of "you". That`s the way this word is usually pronounced in (faster, colloquial) everyday speech when the word is not stressed.