That's an excellent question! You mean that the T sounds like the short R is some languages like Spanish. It happens in words like "butter". Here are some good explanations - and it's called the "flap t": http://www.antimoon.com/how/flap-t.htm http://www.rachelsenglish.com/video-category/flap-t

It isn't. The letter 't' is never pronounced like an 'r'. Sometimes, when a 't' is between two vowels, it can sound close to a 'd' sound. This is a particular feature of US and Canadian English, but it also occurs in other varieties of English.

I agree with Danielle. If you think R and T are similar in English, then you're definitely pronouncing one of those sounds wrong. It's not a good idea to substitute sounds from another language either. It just creates a habit of mispronouncing words. You're far better off learning the proper sounds in English.

Never