English in particular is difficult to learn because it does not always follow grammar rules and you just have to learn when the rules don't apply. Growing up speaking it, you learn what is natural to say, even if it is not grammatically correct, or is correct but deviates from the rules. Also, all English speaking nations have their own version of English, which differs from 'genuine' English. Such as the USA, Canada, Australia, New Zealand etc. Then to make matters worse, within the UK, the language is very regional so different regions speak differently. You can equate this to Spanish which is different in each south american country, to 'genuine' Spanish spoken in Spain. My Colombian Ex-Girlfriend could tell which country in South/Central America someone was from by the way they spoke and their accent. But the first time she heard someone from Spain speak, she had no idea what the accent was!