How can I change the language in Ubuntu?

I am having trouble with the language section in Ubuntu!
I’m a beginner in Ubuntu and I want to install Bulgarian language. I used to have Vista and I installed Flex Type, chose my language and clicked CTRL key and it used to change back and forth from English to Bulgarian. I don’t know how to do that in Ubuntu.I know you go to System-> Preferences-> Keyboard->Layouts->choose your language. But then when i tired that i only write in Bulgarian on application. I can’t write in Bulgarian on the web.I want to have Bulgarian and English language on my computer, but How? Please tell me what I have done wrong. THANKS