Personal disclosure first. I am by education primarily a linguist, so this sort of thing invariably piques my interest. It also no doubt explains why I am such a compulsive spelling and grammar Nazi.
I'm also going to seize the moral high ground for myself, being a born and bred UK national. If forced, I'll grudgingly admit that you citizens of the US, Canada, South Africa, Australia and New Zealand don't make too bad an attempt at using the spoken and written language - but I perhaps should be more charitable. The language itself is called English - as in England - so what real hope do all you ex-rebels and colonials have?

Anyhow, back on point... English is as we know the international language (unlucky, Esperanto

My Japanese friend politely listened in agreement, but then pointed out the core difficulty with English for foreigners - and that's pronunciation, especially of vowel sounds. Trying to place myself in his shoes and thinking about it for a while, he was absolutely right. Consider the simple English construction "ough" for a second. That can be correctly sounded in at least six different ways, to rhyme with "uff", "ooo", "owe", "off", "ow" and "awe", dependant solely upon the word in which it's appearing. That's not simple at all - there's no logic or rule and hence this can only be learned by memory.
All of which brings me to the following small poem by Bennett Cerf, a mid-20th century English humourist (yes, "humourist" does have a bloody "u" in it!), which I thought I'd share:-
Bennett Cerf wrote:The wind was rough
And cold and blough.
She kept her hands inside her mough.
It chilled her through,
Her nose turned blough,
And still the squall the faster flough.
And yet although
There was no snough,
The weather was the cruellest fough.
It made her cough,
(Please do not scough).
She coughed until her hat blew ough.
It shook the bough.
I don't know hough
She got warm again - the silly cough.