"I named it Roland because I wanted it to sound the same in other languages..."
"But, but... English speakers read it as Roland. Japanese speakers read it as rorando."
"Yes, exactly. Same thing."
Another funny story is the Nikon's single lens reFlex camera, the F: it was called than instead of the Nikon R because of the L-R "problem".
So, he can (of course) physiologically hear the difference, but he wasn't conditioned to listen for it. There are features like that for me in other languages (tones in Chinese, as one glaring example).
There are no humans that "can't" hear the difference between L and R.
But there are languages that don't have both sounds.
Just like English-speaking people usually being unable – or unwilling – to say the soft T sound in た、て、と but it's not like you can't hear the difference: [0].
You'd be surprised.
There are no 100% objective sounds the ear directly hears -- interpretation and identification of sounds happens at the brain, and a person that was raised with a specific language/pronunciation can be "deaf" to the difference of certain sounds.
Evidence from Best & Strange (1992) and Yamada & Tohkura (1992) suggest that Japanese speakers perceive English /r/ as somewhat like the compressed-lip velar approximant /w͍/ and other studies[4] have shown speakers to hear it more as an ill-formed /ɺ/. Goto (1971) reports that native speakers of Japanese who have learned English as adults have difficulty perceiving the acoustic differences between English /r/ and /l/, even if the speakers are comfortable with conversational English, have lived in an English-speaking country for extended periods, and can articulate the two sounds when speaking English. Japanese speakers can, however, perceive the difference between English /r/ and /l/ when these sounds are not mentally processed as speech sounds. Miyawaki et al. (1975) found that Japanese speakers could distinguish /r/ and /l/ just as well as native English speakers if the sounds were acoustically manipulated in a way that made them sound less like speech (by removal of all acoustic information except the F3 component). Lively et al. (1994) found that speakers' ability to distinguish between the two sounds depended on where the sound occurred. Word-final /l/ and /r/ with a preceding vowel were distinguished the best, followed by word-initial /r/ and /l/. Those that occurred in initial consonant clusters or between vowels were the most difficult to distinguish accurately. Bradlow et al. (1997) provide evidence that there is a link between perception and production to the extent that perceptual learning generally transferred to improved production. However, there may be little correlation between degrees of learning in perception and production after training in perception, due to the wide range of individual variation in learning strategies.
The same can happen with colors (for them, depending on whether the language/culture has a name for them).
So what you write is not 100% true. At best, it's debatable:
https://en.wikipedia.org/wiki/Perception_of_English_/r/_and_... l/_by_Japanese_speakers
https://en.wikipedia.org/wiki/Linguistic_relativity_and_the_...
https://eagereyes.org/blog/2011/you-only-see-colors-you-can-...
https://en.wikipedia.org/wiki/Blue%E2%80%93green_distinction...
https://www.businessinsider.com.au/what-is-blue-and-how-do-w...
R and L are way more similar.
So I can say "the" with a "th" that sounds like "thanks", or "theater" that sounds like "the" and nobody will be able to tell the difference? Imagine me saying "that" as "thatch". No one would think I have a lisp? No one would say I'm not a native speaker? You know that's BS, unless you said can't perceive instead of can't hear.
It's easy to think that the way we think about sounds is perfectly natural, except that it isn't. The reality is that it's all relative. I'm sure the tones in Chinese come naturally to you but to the rest of us it's a challenge.
As for R and L, Japanese speakers can certainly hear the difference, but it's hard for them to remember or pronounce the difference. Believe me I've tried to explain it many times, and when you try you realize the difference is more subtle than we always assumed.
Korean has more vowel sounds than English. We can hear the difference, but feel convinced that it "doesn't matter" and that "those sounds are practically the same". And it's devilishly hard for us to consistently get the sound right. And that's what R and L are like.
In some words, either the voiced or unvoiced variant do not have an assigned meaning, but you must use the correct one.
In some cases, there is a near clash. For example, "thin" and "then" have a different vowel, which is clear when they are enunciated clearly. However, when it's an unstressed vowel in surrounding speech, particularly fast speech, the difference relies much more on the leading consonant, because unstressed vowels in English gravitate toward the central [Ə] sound.
There are also situations like "this'll" (contraction of this will) versus "thistle".
Learning to hear the difference between ship and sheep took me a long time, and it's the same for everyone I know. Most of my friends who are not regularly exposed to english still fail to notice it or pronounce it.
The same for learning to hear the difference between "a" and "o" in hungarian.
Of course everybody can learn to hear, but it's definitely non-trivial. Your brain just isn't wired to look for the difference, even if clearly the sound is there.