I have heard claims of English being both very easy and very difficult to learn for L2 learners (in adulthood).
Is it that the English writing system is difficult to learn while the language itself is relatively simple? How does it compare to other European languages for non-European L1 speakers?
I think the most difficult thing in English is phonetics. While I can read and write in English well, I still cannot understand anything the news outlets say on the TV, not to say to understand any song. It is also a heavy effort for me to speak English, especially the vowels, actually I never know how each vowel should be pronounced so often people do not understand me. I totally do not recognize, and even understand any difference between "a" as in "pay" and "e" and between "ee" as in "sheep" and "ship".
Also I have difficulty in pronouncing the "th" sound, both voiceless and voiced variety, but this is not difficult to learn, it is difficult to produce, even if I do know the difference.
The syntax and morphology of English are quite easy, but some difficulty is in learning idiomatic sequences of verbs and prepositions, such as "put up", "give off", "put out", "turn down", "set in" etc.
The writing system is totally irregular so one cannot guess the pronounciation from spelling and vice versa, but this is while annoying, is not the most difficult thing.
English is also annoying with its difficult to pronounce numerals, especially when need to speak quickly.
Really, it depends on what language you're coming from.
For example, a lot of people struggle with the phonology of the language because there is a lot more to it than their native language. If you're coming from a language like Spanish with a whopping five vowels, it can be difficult to get a hang of the 21 vowels, give or take, that we have in English. I know speakers of Romance languages that have been in the US for decades and still struggle to contrast certain vowels. The same can be said for /θ/ and /ð/ (the "th" sounds), which aren't super common across languages and can be hard to pronounce if you aren't used to it. However, this doesn't make English "easy" or "hard" to learn, because any language you learn is going to have new sounds that you struggle with. The vowels and some consonants are a struggle for some Spanish speakers, but Arabic speakers won't have much trouble learning the consonants of English, because most of the "hard" English consonants are in Modern Standard Arabic.
For some learners, the biggest struggle is grammar. Many Europeans learn English and think that the grammar tends to be simpler because there is no gender, verb conjugation is a lot simpler, etc. However, if your native language is Mandarin Chinese, a language with extremely simple morphology compared to English, then learning to put "-ed" or "-ing" at the end of verbs and to put determiners in front of words (like "a" and "the"), is going to be a struggle.
Really, it's impossible to speak in general terms about why English might be considered "easy" or "hard." It depends entirely on your native language. What's easy for one group of learners (Romance language speakers learning the grammar rules) could be a struggle for another (Chinese speakers learning grammar).
Fortunately, I have Spanish and English as mother tongues. Both of them seem natural to me, and can switch from one another without much trouble. Thanks to that, I get to see English from in- and outside. Here's what I've noticed:
English is simple because:
English is difficult because:
That is what I know from my own experience. English is a language that you learn by use. I am learning German and took some French, but the demand for practical use might not be as necessary. I believe that may be due to the "rulelessnes" of it.
Also, the short story behind the alleged conciseness of English goes as follow: French come. French conquer. French becomes the official language. People don't like French. People speak as fast and concretely as possible in English. English gets shorter and shorter, considering it is illegal. Finally no more French. English remains short.
Foreigners who say English is easy also often claim in the same breath that it "has no grammar." What they mean by that is that each word has relatively few forms that need to be learned. Irregular plurals and irregular verb forms are fairly limited in number. If you compare this to French, where people need to learn numerous conjugated forms of verbs, you'll see the difference. Since the memory of learning conjugation tables is emblematic for many people of the negative experience they had in school learning some language they may never have made any progress with, they tend to associate that kind of learning with what they consider difficult languages.
But there is of course much more than that to grammar, and that kind of morphology is usually not the hardest part of learning a language competently. When it comes to deciding which verb form to use, I've observed that second-language speakers probably make more mistakes in English than they do in French (sorry for the unscientific answer). Phrasal verbs are an additional difficulty, and I believe learners need to be very advanced before they can really get a good feel for the meanings of the particles. (They might know "butter", but would they "butter" their boss or "butter him up"?)
All in all, I would say I've seen more second-language speakers with near-perfect French than near-perfect English. This is perhaps less true as regards immigrants; I mainly have foreign-language speakers in mind.
These days, there is one important way in which English may well be easier than practically any other language, for most nationalities anyway. That's that you've already learned hundreds of English words before you so much as set foot in a classroom. This is because in many countries advertising uses English words, there may be many borrowings from English in the language, and it tends to be present in people's visual environment for other reasons too (for example, if they go to the default webpage for a multinational company).
I would hypothesize that Americans have a head start in Spanish for the same reason, making it easier to learn for them at the initial stage than Portuguese, for example. I'm not sure how much of this is the learning actually being easier as opposed to a kind of emotional response to seeing familiar words come up. I don't think there are many Americans who don't know that el, la, los and las mean "the" in Spanish, at least passively. How many know the corresponding words in Portuguese? If you are learning Portuguese, it won't take long to learn them, but it may feel good if you don't have to.
From my experience teaching English as a second language, many students feel overwhelmed by the flexibility of English. There are many ways to say similar things, and the students often long for 'right' or 'correct' ways to say something. The flexibility of English makes for less rules (easy) but maybe also less structure (difficult), compared to many first languages.
