I think its extremely important in the United States. The US is a "melting pot" of cultures. No one cares if your back ground family history is from Poland, Brazil, the north pole. If you can speak english they can identify with you.
I think its important for the fighter to be able to speak the native language of the country his industry is based in. You must remember that this is above all part of the ENTERTAINMENT INDUSTRY. Its all about marketing, speaking with your fans is very important.
Im not saying this to bash Sliva. Im saying this because above all in the US I feel this is important. The title holders are the stars. The stars are what draws people in. The people want to be able to speak and indentify with the star fighters. You cant do that through a translater, at least not as well.