While the “R” is in the same position but with the tongue allowed to drop a little so that it “floats” ever so slightly below the palate. The Asian “R” becomes an “L” simply by touching the palate with the tongue. That's why L and R sound so similar to our Western ears – because they are very similar.
In Mandarin Chinese, /r/ sounds are not made using the American /r/ sound (as in car). The Chinese /r/ sound is made in the same way we make the sound in the word 'leisure' (in American English). This is called a retroflex /r/ because the tongue turns back toward the throat.
The /l/ can only appear syllable-initially while the /r/ appears syllable-finally. This means that a Chinese speaker would have more trouble with an /l/ sound at the end of a word and also with an /r/ sound at the beginning of a word.
Erhua (simplified Chinese: 儿化; traditional Chinese: 兒化; pinyin: érhuà [ɚ˧˥xwä˥˩]); also called erization or rhotacization of syllable finals) is a phonological process that adds r-coloring or the "er" (注音：ㄦ, common words: 耳、尔、儿) sound (transcribed in IPA as [ɚ]) to syllables in spoken Mandarin Chinese.
In native Korean words, ㄹ r does not occur word initially, unlike in Chinese loans (Sino-Korean vocabulary). In South Korea, it is silent in initial position before /i/ and /j/, pronounced [n] before other vowels, and pronounced [ɾ] only in compound words after a vowel.
"I agreed that in Japanese, they spelled both English "L" and "R" with "R". But it will be incorrect to say that they have trouble to pronounce "L". It is actually the other way around, that is, they have trouble pronouncing "R". They simply don't curve their tongues.
In Korean, the “l” and “r” sounds come from the same underlying consonant ㄹ. If you put your tongue in between making an “l” and making an “r,” you're almost there.
Rieul (sign: ㄹ; Korean: 리을, rieul) is a consonant of the Korean alphabet. The Unicode for ㄹ is U+3139. Rieul is pronounced [ɾ] at the beginning of a word and [l] at the end of a word. For example: 러시아 reosia ("Russia"), 별 byeol ("star").
Where words like saw and idea come before a vowel, there's an increasing tendency among speakers of British English to insert an 'r' sound, so that law and order becomes law-r and order and china animals becomes china-r animals. Linguists call this 'intrusive r' because the 'r' was never historically part of the word.
The light tap is often perceived as an R by other speakers, and this is why it seems like the R's and L's are confused (even though it's not the English R). When Korean speakers hear the R in English, they often categorize it as L, which makes it really hard for them to distinguish between the two.
Some sounds are not in their language
In some cultures and often Asian cultures the sounds around them are so completely different to the English sounds, the people's tongues literally grow comfortable in a certain way and it is very difficult to retrain it any other way.
“R” is a definitely hard pronunciation for Koreans. But, we have a similar sound “ㄹ.” Even though English language doesn't have the exact same pronunciation as “ㄹ” I would say “L” corresponds to double “ㄹ” in Korean.
Rhotic accent (pronounced / /) speakers pronounce a rhotic consonant-r in words like car, bar, far, hard, farm, and first. Non-rhotic speakers, for example, speakers of British English (BrE) and Australian English do not articulate the /r/ in all of such words.
In Korean, there are no F, R, V, or Z sounds, so let's take them out.
If the consonant ㄹ[rieul] is between two vowels, then it'll usually have the English “r” sound. However, if it's at the beginning or end of the word, or precedes a consonant, it'll have more of an English “l” sound.
A common struggle that Koreans have with pronunciation is with the L and R sounds. This is because they use ㄹ, which is somewhere between L and R. When writing down English words using Korean characters, this letter is used for both L and R, making Koreans accustomed to using this sound to replace both letters.
Japanese has one liquid phoneme /r/, realized usually as an apico-alveolar tap [ɾ] and sometimes as an alveolar lateral approximant [l].
Three-quarters of the world's languages have at least one 'r' sound – what linguists call a rhotic.
People with rhotacism typically produce the /r/ sound as a vowel-like sound, and this makes the /r/ word hard to understand. Often the /r/ is pronounced like a “w”. For example, “Roger Rabbit” tends to sound like “Woger Wabbit”. Rhotacism can also make other sounds difficult to distinguish.
tl;dr: It varies, but it is usually a weak "b". It varies from person to person, so some may pronounce it like the English "v", but others may use a strong "b" sound. Originally, Japanese had no ヴ character so they used variations of ビ (bi).