Speaking of Asia, why do so many Americans think that Asians mix up R and L? (Asians? East Asians? Chinese and Japanese? How far does this stereotype go?)
Before we answer this question, I need to point out a more general misconception that many non-linguists have about language: they think that written language is language. In fact, language is primarily speech, not writing. Writing is merely an imperfect representation of speech.
Nobody is mixing up the letters R and L.
Someone might confuse one of the sounds that R represents (there are many!) with one of the sounds that L represents (there are many!). And perhaps that person is a speaker of Cantonese, or Mandarin, or Korean, or Japanese, or… Or perhaps the problem lies with the perceptions of the American listener.
For a full explanation, watch this compelling video. The situation isn’t as simple as you may think, so you should probably watch it twice!