For anyone wondering, salmon's pronounciation comes from the French word saumon. The French word comes from the Latin word salmo. When smarty pants scholars decided on how words would be spelled in the middle ages, they thought salmon should have an L in it since the Latin word does (screw with all those dumb people who don't know Latin!)
In case anyone else who isn't knowledgeable in Latin is curious as to what "salmo" means and why they decided to name a fish after it... Salmo means Salmon.
There's a bunch of words spelt annoyingly because those bastard scholars decided they'd like to incorporate the historic roots of words, rather than the reality of words, in their spelling.
Yeah it turns out a whole bunch of English words are spelled more like a linguistic history lesson than anything approaching a useful system of phonetics. It might as well be pictographic with letters being helpful hints at this point. I wish there could be spelling reform in the anglosphere, but it's hard enough to get people to agree within any one of the majority English-speaking countries, let alone between them.