English vowel system is the most terrifying stuff. And if it wasn't bad enough, it varies between regions and it even changes over time
BTW in Spanish we have one silent letter, H. The rule is that it's -always- silent, lol.
Your changes a lot as well though

I don't speak Spanish, but AFAIK s in Spain (Ethpaniol) is pronounced th while in most other Spanish speaking countries it is s.
Dialects are awesome though and the differences in English are pretty slim. I think the various Chinese dialects are so different without a common written language they wouldn't understand eachother.