A question asked:-
Yahoo answers :-
In ettiquete, it is considered to be EXTREMELY RUDE to be talking in a foreign tongue in the presence and company of others who can't speak the language. If you think about it, it is sort of morally degrading - you are speaking in a tongue others cannot possibly understand and comprehend; it looks as if you are trying to show off your skills and your ability to speak in a different language.
It is worst still to be speaking in a foreign tongue when the company of people you are with can speak English**. To the people around you, it may seem like you are talking about something that you do not want them to know about. If you really must talk about something, politely excuse yourself. That's the way to do it instead of openly flaunt your so-called "language" skills.
Hence, yes - I think it's VERY RUDE. When you are in the company of people who can speak English** and you are speaking your own dialect of languages - you are considered to be ill-mannered. Speak English!** We're all listening!
"SATU BANGSA, SATU NEGARA, SATU BAHASA"
** For Malaysians, replace "English" with "Bahasa Kebangsaan".
You are Malaysians,