- b, v and sound like /b/, because v lost its original pronunciation and w was lent from other languages.
- h lost its sound and became silent (used to be a soft /f/).
- g can sometimes sound like /j/ (there was some pressure to remove these uses).
- x can be an /s/ at the start of a word (due to Greek ancestry).
Those are considered mistakes, but they do not change the pronunciation of the words.
For the concrete rules: https://www.rae.es/ortograf%C3%ADa/valores-fonol%C3%B3gicos-.... You can see the exceptions to "one letter, one sound" are very few.
- b, v and sound like /b/, because v lost its original pronunciation and w was lent from other languages.
- h lost its sound and became silent (used to be a soft /f/).
- g can sometimes sound like /j/ (there was some pressure to remove these uses).
- x can be an /s/ at the start of a word (due to Greek ancestry).
Those are considered mistakes, but they do not change the pronunciation of the words.
For the concrete rules: https://www.rae.es/ortograf%C3%ADa/valores-fonol%C3%B3gicos-.... You can see the exceptions to "one letter, one sound" are very few.