If written in kanji 紅茶 (こうちゃ) combines the characters for crimson (or deep red) and tea. Black tea would therefore be the most appropriate translation. Although in some cases it can mean "western" teas in general such as herb, fruit or black teas as opposed to "japanese/asian" teas お茶 (おちゃ) in general such as oolong, barley or the various green tea varieties.
Yea in the US if you just say tea you will most likely be given cold black extremely sweet tea, unless you are specific. Like can i get a hot tea and then it will be either plain hot black tea or else they will offer you different kinds.
As far as barely tea though, I feel like its only popular in Asia. I havd never heard of it before, but my wife is Korean and she loves it. Her moms makes it all the time, but I hate it. So gross.