unicode/two-byte characters question

I am interested in getting some info on how unicode/two-byte characters work in most databases. I believe two-byte characters in Asia is quite common. My questions are: How many spaces I should declare in varchar for 50 unicode/two-byte characters? In varchar(n), n represents number of bytes or characters? is it correct to declare varchar(100) for 50 unicode characters? Or can this handled by configuring the character set? What character set should I use? Thanks, Leslie