That's because they mangle their own language awfully enough.
I'm not a native English speaker but I've heard quite a few native Englishmen and their accents are horrible. Received Pronunciation is obviously nice to hear and quite clear, but those local accents... oh my!
I'm not saying that my accent is any better, but at least I try to make my sounds be as close as possible to the actual letters used in the word! :)
This is simply due to the language having been heavily influenced by a host of other - quite different - languages over the centuries, Old Norse and French in particular.
There's also the interesting fact that as the first human language in history English is spoken by more non-native speakers than native speakers. Some linguists say we might very well see some sort of International English that's highly influenced by foreign accents.
In fact there already is such a variety although it's only used by a rather small group of people: The kind of English used by the European Union, its officials and bureaucrats. EU English is littered with bureaucratic expressions, loan words and false friends (particularly from French).
"The problem with defending the purity of the English language is that English is about as pure as a cribhouse whore. We don't just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and rifle their pockets for new vocabulary."
It's actually worse than that. I see that the Great Vowel Shift has been linked to, but it's probably not immediately clear why that was significant.
What happened was that "between 1350 and 1600.... all Middle English long vowels changed their pronunciation". Unfortunately this occurred just as spelling was being standardised, so some spelling was standardised using the old pronunciation (which then shifted) and some with the new.
There is, it's just very complicated (hundreds of rules), as well as accent-dependent, and there are lots of exceptions.
It's the spelling that is irregular.
When you first hear it you think it's a different language.
In fact, it's almost impossible NOT to spontaneously invent a pidgin when there's a language barrier between two people or peoples. When I was in Vietnam, my friends and I adapted our English ad-hoc depending on who we were speaking to. With merchants with very little English, we'd speak only in numbers and yes/no, and maybe say please/thanks in each others' languages. With our tour guides who were much more fluent, we could speak in complete sentences, but still tried to keep things in present tense, and tended to ask questions by using a declarative word order with a rising tone ("we go to the hotel now?").
And we did this all instinctively--it's easy to see how well-defined pidgin languages can arise from this sort of linguistic adaptation between two or more populations.
Na craze talk be dat
However, in the Early Middle Ages English was also heavily and directly influenced by Old Norse because Vikings at that time not only more or less continually invaded the English east coast but also settled and established their own jurisdiction (The Danelaw) there.
So you'd pronounce "ghoti" as "fish" then?
The point is that the "letters used in the word" are a really bad guide to pronunciation of English. They're not consistent across words or the place of the letter within the word. It's just consistent enough to make people think that might be the case.
Then you get placenames like "Loughborough", "Worcester", "Bicester", "Cholmondeley", and "Slough".
> However, linguists have pointed out that the location of the letters in the constructed word is inconsistent with how those letters would be pronounced in those placements, and that the expected pronunciation in English would sound like "goaty"; [ˈɡəʊti].
> Whenever the subject comes up, someone is sure to bring up all the words in -ough, or George Bernard Shaw's ghoti-- a word which illustrates only Shaw's wiseacre ignorance. English spelling may be a nightmare, but it does have rules, and by those rules, ghoti can only be pronounced like goatee.
But it's the only available clue, so people will use it!