They are different languages
and use different orthographies because they have different phonologies and different phonotactics (and histories, conventions, traditions and customs).

They might use the same (or similar) symbols, but the symbols have different meanings.

As an aside. English has about a dozen vowel sounds plus about 6 diphthongs, and 24ish consonants (varies a little due to dialects, and how generous you're feeling). However, we only have 26 letters. So we have rules like digraphs (two letters, one sound) such as the ou in sound or the th in the or the ow in tow, and thing like adding an e like in like or in came, to change vowel sounds.

However, a nice simpler language like Italian has about 7 vowels, a couple of diphthongs, and about 15 consonants. They use the same alphabet as English (but only use 21 letters and the other 5 just in foreign loan words). So fewer sounds, but about the same number of letters. So they have different rules. An English word pronounced using Italian rules sounds different. Come would sound something like comma. And vice versa, bruschetta is pronounced in Italian as something like broosketta, since u represents always the sound of u in (roughly) rule, and ch is always pronounced /k/.

It has been theorised that (vulgar) latin only had 5 vowels (with length distinctions), hence the 5 vowels in our (latin) alphabet...
( Sextant goes to him is emotionally erect, on this day, Fri 9 Apr 2010, 13:54, 1 reply)

this proves
that language is a strange thing
( Smash Monkey lowering the tone of the whole internet, Fri 9 Apr 2010, 16:15, closed)