If they speak another language besides English, they only tend to speak their native language (s) to those that only speak that/those language/languages. I'll give you a couple examples.
- My best friend's first boyfriend was Cuban. However, he was ok with only speaking English with her and only spoke Spanish to his parents or those that didn't speak English at all.
- I once dated a Brazilian guy and foolishly thought he would teach me some. I learned a couple phrases to impress him but was ok with only speaking English with me.
- My own cousin (she speaks Italian, French and Spanish) only speaks those language if the person doesn't know English.
Why do you think they don't want to teach us their beautiful languages? They know English and that's all they want to speak to us.