With English, you have not only differences between countries, but within the U.S. there are a phenomenal number of regional dialects. You not only have Northeast vs the Deep South vs West Coast, but within Alabama, I can tell a distinct difference between northwest Alabama, Northeast Alabama, and the Birmingham area. But I suppose this is true of most languages.
All very true, but before we even get to that, I was thinking of the fact that letter combos in English aren't pronounced consistently depending on the word and where in the word that combo falls. Just as an example: -ough can be "uf" as in "enough" or "-off" as in "cough." And "fish" can be spelled "ghoti" if you really want to.
In British English, I believe you can technically spell "fish" as "ieuoti," borrowing from the pronunciation of "lieutenant." Dr. Seuss also wrote a book called "The Tough Coughs as He Ploughs the Dough," illustrating how difficult it is to predict how words are pronounced in English.