Spelling and pronuciation in English

I have frequently marvelled at the seemingly unnecessary complexity of English orthography. It must be extremely confusing for anybody trying to learn English as a second language to get their heads around the the very different pronunciation of "ough" in the words enough, bough and through.
I believe a major reason for this was that writers were free to "invent" their own spelling for words and that no standards were set until Johnson's dictionary first appeared in 1755.
In this context, I came across this wiki entry which includes a very interesting poem which nicely encapsulates many of the orthographical inanities of the English language.

I take it you already know,
Of tough and bough and cough and dough.
Others may stumble, but not you,
On hiccough, thorough, laugh and through.
Well done! And now you wish, perhaps,
To learn of less familiar traps.
Beware of heard, a dreadful word,
That looks like beard and sounds like bird.
And dead - it’s said like bed, not bead,
For goodness’ sake, don’t call it ‘deed’!
Watch out for meat and great and threat,
(They rhyme with suite and straight and debt).
A moth is not a moth in mother,
Nor both in bother, broth in brother.
And here is not a match for there,
Nor dear and fear for bear and pear.
And then there’s dose and rose and lose –
Just look them up – and goose and choose.
And cork and work and card and ward,
And font and front and word and sword.
And do and go and thwart and cart –
Come, come, I’ve hardly made a start!
A dreadful language? Why man alive!
I’d mastered it when I was five.