Mrz:
^In English a sound can be written with one, two, three or four letters, the sound /ai/ can be spelt in apron in train or as in weight for example.
A sound can have different spellings - see beat money he fiels Ian Amy either Steve paediatrics
The same spelling can represent different sounds bread, beat & break.^
Most people are probably aware of that.
But these irregularities are NOT BECAUSE
We only have 26 letters in the alphabet but spoken English has roughly 44 sounds.
The shortage of letters can be overcome by combining some of them (ai, ch, sh). And if done in a regular, predictable way, English would have just 44 spellings for its 44 sounds. Perhaps something like
a, ai, air, ar, au, b, ch, d, e, ee, er, f, g, h,
i, ie, j, k, l, m, n, ng, p, o, oe, oi, oo, or, ou,
r, s, sh, t, u, ue, v, w, y, z, si,
and one for the unstressed half-vowel, as in 'decide, flatten, flatter'.
It could do with unique spellings for short oo (could put wood) and the two th sounds (thing thing) as well which it hasn't got despite using a huge number of different graphemes.
English has gradually become further and further removed from the alphabetic principle of spelling speech sounds in a regular, predictable manner, with 205 spellings for 44 sounds. Because of this, learning to read and write the language now takes an exceptionally long time and is EXTREMELY DIFFICULT for roughly 1 in 5 children.
Although some of the irregularities are due to borrowings from other languages, without anglicising their spellings (as used to happen earlier: beef, mutton, battle), many of the irregularities, such as mOnth, wAs, thrEAd, were created quite deliberately by scribes and printers who did not give a fig for ease of learning.