I will preface this with the fact that I have some symptoms of asperger's and so, it's easy for me to make faux pas social situations, and difficult for me to judge what would be rude or not.
I think when one begins to learn a language there is a certain level of enthusiasm or excitement so it's natural to want to use it wherever one can, but also I think there may need to be some level of restraint.
Can it be considered rude or offensive to just start speaking mandarin if I don't know the person well enough?
Assume I'm in England or another English speaking western country and I've started conversation in English in a natural and polite way with, for example a shopkeeper, hotel staff, at a restaurant etc.
I'm clearly a white british person and the other person has no idea I know any mandarin just by looking at me.
Without intending to sound racist in any way, shape or form, there are certain cues one can pick up on, like the appearance of someone and whether or not they speak with a Chinese accent. If I pick up on these cues, can I just start speaking mandarin?
The reason I think it may be considered offensive is because if I do not know the person well enough then they may think I'm assuming too much about them. Also I think possibly if one starts speaking mandarin based on appearance alone it might be considered racist.
It also might be a bit too intimate for someone to speak with a stranger in their native language in a western country.
On the other hand, a chinese friend of mine said that if white british people started speaking to them in mandarin their reaction would be surprised and happy.