When I watch Anime, I notice that Japanese English pronunciation is really bad, they twist all the sounds, and they can't pronounce sounds like "L". I think English is the easiest language when it comes to pronunciation, and I don’t think it has something related to their native language, as for me, I learned Arabic,French and English, and I have no problems with the pronunciation, even though my mother language (Tamazight) has nothing related to these languages.
English pronunciation isn't easy
Don't think that, just because you find it easy, most people in the world will; English pronunciation is actually quite complex by any measure. The language has something around 10 vowels (not counting diphthongs) and 44 phonemes; well above the average, and more than double Japanese's 5 vowels and 17 phonemes. What's more, English syllables are unusually complex, and may have long sequences of consonants (as in "lengths") and consonant-only syllables (as in "bottle"). Even people in Spain or Italy will unconsciously add vowels between the consonants in order to simplify English syllables—and Japanese syllables are even simpler.
People generally have trouble with foreign sounds
You say you find it easy to pronounce sounds not in your native language, and I don't doubt you. However, you're being unfair to the Japanese by singling them out; just listen to second-language speakers anywhere in the world, and you'll find that people generally have trouble distinguishing sounds not in their languages. For example, the Chinese speakers I known find it difficult to distinguish sounds like b/d or e/ɛ when learning my native Portuguese. English gringos have trouble with the nasal "ã", or even with saying a simple /o/ without turning it into a diphthong [oʊ]. I have trouble with English t/th; anyone from a non-tonal language has trouble with Chinese tones, and so on and so forth.
Of course, people can learn these sounds (if properly instructed); but it's a well-known fact that many don't, even after years living in another country. This is interesting, because babies always learn all the sounds people speak around them (well, except for a few cases of "speech dysfunction", like lisps; but these are unusual). Adult foreign learners have a lot more difficulty.
English is incorporated into the Japanese sound system
Did you know that around 58% of English words came from Latin and French? But they pronounce them very different than actual Latin or French. The word "Latin" itself, for example, is like [ˈlæ.ʔn̩] rather than /ˈla.tin/. Et cetera is /ˌɛtˈsɛtɹə/ instead of /ɛt ˈkeːtera/, and so on.
My point is, when you incorporate lots of words from a foreign language into your own, you adapt the pronunciation to fit yours. It would be a bother to keep changing from English sounds to Latin sounds all the time.
Japanese has something like 30% "foreign" (gairaigo) words (not counting Chinese), most of which are English. Just like English speakers adapt words like "Et cetera", "Paris" or "Mexico" to fit their own sound system when speaking English, Japanese adapt English words (and others) to fit their own sound system when speaking Japanese. So "hamburger" becomes hambāgā, "cut" becomes katto, etc.
Unfortunately, this means Japanese people have an easy-available but inexact "version" of English already in their minds, and this makes it harder to learn actual English pronunciation. When English people learn Latin, they have to begin by unlearning the way they pronounce Latin words and Latin letters, and get used to actual Latin sounds. Japanese people, too, have to learn to set aside their native gairaigo pronunciation.
If the Japanese person needs to actually speak English, for example to live in England, they will learn it; but if they're just living in Japan and talking to other Japanese people, they'll just use the Japanized English words, for the same reason that English speakers use an Anglicized pronunciation of Latin words when talking to each other.
English classes in Japan usually suck
Japan has mandatory but atrocious English education, which is worse than no education. Richard Schmidt has pointed long ago that foreign learners won't acquire non-native sounds unless you draw conscious attention to them first. However, the typical English course in Japan doesn't try to teach the basics of articulatory phonetics or how to enunciate the sounds; they just keep doing grammar drills and such. I'm living in Germany, and I got a Japanese student to pronounce German-only sounds like "ö" and "ü" in one afternoon by explicitly explaining tongue and lip positions to her. I'm sure that, if a Japanese person is actually taught English phonology, they'll be able to pronounce English without major issues. I've met plenty of Japanese individuals with better English pronunciation than mine (admittedly, they usually have lived overseas, and therefore had incentive to learn actual English pronunciation, as opposed to their native Japanized English).
Here's an answer from developmental psychology:
When a baby is born they can natively pronounce phonemes of every language, but as they develop, their brains are constantly calculating and keeping track of which phonemes are more often said. This causes the baby to lose their ability to natively pronounce or even differentiate other phonemes except the ones spoken in the languages of their environment. This does mean that biracial babies will be able to pronounce more phonemes natively.
After what is known as the "critical period", it is very, very difficult to retrain the brain to learn to pronounce/differentiate new phonemes.
Quote from Neuroscience, 2nd Edition, specifically answering about the pronounciation of the l/r:
Very young human infants can perceive and discriminate between differences in all human speech sounds, and are not innately biased towards the phonemes characteristic of any particular language. However, this universal appreciation does not persist. For example, adult Japanese speakers cannot reliably distinguish between the /r/ and /l/ sounds in English, presumably because this phonemic distinction is not present in Japanese. Nonetheless, 4-month-old Japanese infants can make this discrimination as reliably as 4-month-olds raised in English-speaking households (as indicated by increased suckling frequency or head turning in the presence of a novel stimulus). By 6 months of age, however, infants show preferences for phonemes in their native language over those in foreign languages, and by the end of their first year no longer respond to phonetic elements peculiar to non-native languages. The ability to perceive these phonemic contrasts evidently persists for several more years, as evidenced by the fact that children can learn to speak a second language without accent and with fluent grammar until about age 7 or 8. After this age, however, performance gradually declines no matter what the extent of practice or exposure.
As other answers note, Japanese and English doesn't necessary have much phoneme overlap
From a very famous and informative TED talk about this topic, that explains that it's very difficult for the brain of a native Japanese to differentiate between an "l" and an "r":
What you see here is performance on that head-turn task for babies tested in Tokyo and the United States, here in Seattle, as they listened to "ra" and "la" — sounds important to English, but not to Japanese. So at six to eight months, the babies are totally equivalent. Two months later, something incredible occurs. The babies in the United States are getting a lot better, babies in Japan are getting a lot worse, but both of those groups of babies are preparing for exactly the language that they are going to learn.
The TED talk even shows demonstration videos on this effect, check it out.
Part of a theory of foreign pronunciation proceeds straightforwardly from David Stampe's theory Natural Phonology. Every natural language is phonetically difficult for a child, because many sounds tend to be changed into easier ones. A child's task is to learn not to let this happen for the languages he must learn to pronounce. See Stampe's article in CLS 5, The acquisition of phonetic representation. The phonological system of a language consists in the set of those those simplifications of sounds, the "processes", which needn't unlearned by children in order for them pronounce their language correctly.
There is a considerable difference between what must be learned by children learning Japanese and children learning English. For instance, children have a tendency to drop word-final obstruents (p/b/t/d/k/g/f/v/s/z/...), and they have to get over that to pronounce English correctly, but to learn Japanese, they needn't bother, because Japanese doesn't have word-final obstruents. This is why Japanese trying to pronounce English drop such obstruents at first. It is simply something they didn't have to learn when learning Japanese as children.
I don't know whether it is available online, but Julie Lovins' dissertation Loanwords and the phonological structure of Japanese is an excellent account along these lines of what we can infer about the structure of Japanese from borrowings of English words into Japanese. See Julie Beth Lovins.
In summary, English words are easy to pronounce for English speakers, because they've learned how to do that, but difficult for Japanese speakers who haven't yet learned how. Pretty obvious, really (though the details are complicated).
There are numerous cultural reasons, here are the primary linguistic reasons imo.
- As was mentioned briefly, Japanese has a very different phonological system than English, virtually all "syllables" are CV or V. Examining this chart of the Japanese mora is very educational of how the system functions. https://en.wikipedia.org/wiki/Japanese_phonology#Phonotactics
Realizing this, one can begin to see how absolutely different a sound system would be where multiple consonants are mashed together into the same syllable, as English does. This, according to several of my friends who speak Japanese, makes Japanese speakers inclined to place vowels in between consonants, which obviously alters the word.
- The simple lack of similar consonants, and vowels, between Japanese & English. This chart, https://en.wikipedia.org/wiki/Japanese_phonology#Consonants , gives all the Japanese consonants and you can see a number of English sounds are missing.
As for the difficulty in pronouncing "l" specifically, you may notice on the chart that there is a weird l-shaped letter and a weird r-shaped letter that are in the same box separated by a squiggly line. This indicates that the sound is a spectrum between the two l & r sounds. This is likely the main difficulty in pronouncing l's in English for Japanese speakers, the sound is split into two! (also note that a similar situation exists in Korean)
Apparently, according to a friend who speaks Japanese, the most difficult phrase for Japanese speakers to say is the name of the movie, Dances with Wolves. I believe this is because the consonant clusters as well as numerous consonants that do exist in Japanese! (such as L)
There's a very good Wikipedia article at https://en.wikipedia.org/wiki/Perception_of_English_/r/and/l/_by_Japanese_speakers
In it, there is the remark 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
Imagine your name is Robert Loyal!
So the next time you think someone from Japan is lamenting lack of beauty ("I ugly"), realize he or she may be saying, "I agree!"
For your amusement, I suggest the poem "The Chaos" by Gerard Nolst Trenité: http://ncf.idallen.com/english.html
While I'm not a linguist I am married to a Mandarin Chinese speaker who learned English in adulthood and I have noticed some very definite patterns in her learning. Specifically, learning new ways of saying something is easy for her (no surprise as she is also fluent in several local dialects of Chinese.) Learning new fundamental language concepts is far harder.
Chinese is spoken by the syllable, not the letter. English speakers learn to enunciate the sounds of each letter and thus have little trouble when faced with a non-word or an unknown word. Consider, for example, "bot". While it does have a meaning out of biology most people did not know it before the coming of the computer revolution--yet a native English speaker would have no difficulty with how to pronounce it.
Chinese, however, does not have this flexibility. As they have only learned to say a specific set of syllables. Their standard written language does not even permit the expressing of alien pronunciation, although it can be done with Pinyin. When foreign things get incorporated into Chinese it is within the context of those syllables--often changing it to the point that it is no longer recognizable (and this cuts both ways--she will often not recognize the proper pronunciation.)
Learning syllables that she did not learn as a child is a much harder thing for her. She once actually told me that Chinese does not have an "r" sound--yet it most certainly does. She did not equate "er" with "r".
While I do not know Japanese it is a descendant of Chinese and most likely suffers from the same limitation.
(And while not actually relevant to the question there is a related issue with concepts. When we have two words that map to one word in Chinese she has a much harder time learning the right English. To this day she still occasionally slips up and opens a light or turns on a door.)
To add to all the above answers, I would like to point out the same phenomenon is to be found even between neighbouring European languages. Sometimes it's a simple matter of cultural politeness.
As a trilingual English-Dutch-Spanish speaker I have observed that while English and Spanish both contain the phonetic θ (thing, paz) and English contains the ð (this, other, smooth), they both require sticking your tongue out of your mouth, beyond your teeth. The Dutch language does not contain any such phonetic that requires that, and also Dutch people learn it is impolite and an obscene gesture to stick your tongue out of your mouth. As a result, and with no other physiological inhibition, the Dutch, most of whom are proficient in English, pronounce both phonetics as 'de' or 'te'. Spanish, even those less proficient in English, have no such problem. It also explains why Hispanics on the American continent pronounce the Spanish θ as 's'. The same of course, goes for the Germans, hence their 'ze'.
After all, English is such a rude language, the English constantly sticking their tongue out towards you.
And to bough down in all humility, I must admit I cannot distinguish between the Spanish 'r' and 'rr' (pero vs. perro). My Spanish wife cannot for the life of her understand that.
This is a really amusing question. I usually think: before someone asks, why does someone speak in a language with accent or that why are they not so idiomatic, flip the coin, and ask: can you even speak 2 or 3 complete sentences in their languages?
Japanese language doesn't have some phonics (vowels and consonants) that is in English. Just like English doesn't have some phonics in Spanish. For example, a lot of Westerners cannot pronounce the word Ng, which is a Chinese last name. So to make it possible for them to pronounce it, it is transformed to "Eng". I heard the theory was that (1) you are not used to saying that phonics all your life, so can you say it immediately if it deviates from your habit (2) when in childhood, some of your bone and joint structure near your mouth is already formed for you to use that phonics system a lot, so if you want to pronounce some different phonics, you are working against your bone and joints to do the job (after you have become an adult).