Salmon and Often
I've often noticed that speakers of English as a second language mispronounce salmon.
It looks like it is straightforward enough to pronounce: sal - mon, but in fact the L is silent. To pronounce it correctly, imagine that the spelling is "sammon". It rhymes more or less with 'famine' even though the spelling is quite different. (English is strange that way.)
On the other hand, 'often' is one of those words that has two accepted pronunciations - with or without the 't' sound. This is not a UK/US thing; the words simply has two accepted ways to pronounce it. There are many words in English like this. Like I said, English is strange.
You can listen to the pronunciation(s) of these words here:
The Cambridge dictionary doesn't give the audio pronunciation for 'often' with a t sound, but it lists the phonetic spelling for it.)