Mandarin Chinese and Cantonese (and presumably most/all other dialects) distinguish r from l. You're thinking of some Japanese/Koreans having trouble due to those languages using a single phoneme that's somewhat between r/l.
Also, it's a bit racist to not point out that it's only some Japanese and Koreans that have trouble pronouncing r and l.
I'm not so sure about the Cantonese/ Mandarin part, since a fair few professors I've had, had those as a native tongue. Hell, even my thesis supervisor was, with whom I communicated extensively. I can't really pinpoint where the struggles lie, but I get the general feeling that for Chinese native speakers there's a three way confusion between n, r, and l, and it's heavily dependant on the placement in the word, as well as the level of stress on the letter.
I don't think recognising phonetic differences between native speakers of different languages is racist. The language I grew up speaking didn't differentiate between w and v, so unless I'm making a conscious effort against it, they will all sound like v's. When someone points it out, I don't find it racist at all.
Re: Koreans - never realised! I haven't had many interactions with people of Korean descent, so it's an oversight on my part there.
