but in French you can usually derive a words pronunciation from it's spelling and vice versa.

I think same goes for every sane language

French is also a proscriptive language. There is a governing body that decides which words are "French" and how they should be pronounced.

English is a descriptive language. Words can be borrowed from other languages, and the only "rule" is common usage. If you speak and you are understood, then that's all that matters. There is no authority or governing body, as much as dictionaries like Oxford, Merriam, and Webster try to pretend to be. That can cause word pronunciations to change over time. There's actually an interesting phenomenon where English words will be "mis"-pronounced because people make up non-existent rules, and if enough people believe it, then the pronunciation becomes correct through popular usage.

Take the word "forte" meaning a personal strength or expertise. It is a word English borrowed from French, and many UK English speakers use the original French pronunciation, which sounds almost exactly like "fort." American English speakers, seeing the word written and thinking it didn't sound French enough, mispronounced the word as "FORtay" and this has become the accepted pronunciation in the USA. Further confusion stems from homonym used in music "forte" which is pronounced "forTEH" because it is the Italian word for "strong" meaning loud or forceful. Linguists sometimes also argue that the US pronunciation caught on because it clearly differentiated the word from the word "fort" meaning a military encampment.

The point is, English has no rules. To quote James D. Nicoll, "The problem with defending the purity of the English language is that English is about as pure as a cribhouse whore. We don’t just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and rifle their pockets for new vocabulary."

In Spanish, you can derive a word's pronunciation from its spelling, but not the other way around, due to letters such as b, v, h, ll and y, some of which are interchangeable or mute.

Yeah, I realized after asking that it's kind of a dumb question, considering I'm a native speaker and I was just writing about how I've mispronounced a bunch of words for most of my life that I've only ever read.