English is a mixture of Saxon, Viking, French and Latin. We have taken words from various languages and tried to adapt them to a single spelling system. 'gh', for instance, used to be a letter that we don't use any more and was pronounced. When the French invaded in 1066, they adapted this to their alphabet, replacing it with letters they used. As a mixture of languages, rather than a pure one, it's a bit of a mess in this area, but it has the advantage of being very flexible.