I couldn't find any information on how Sweden lists salt/sodium on labels. Is the "salt" listing higher than the sodium?
What we call salt is actually sodium chloride, so a gram of salt doesn't have exactly a whole gram of sodium. Also, the word salt actually means a type of molecule. Sodium chloride is the most common example, but there are other salts like potassium chloride. So I would guess that the Swedish government has asked the manufacturers to separate out salt from sodium. The difference would be really small in most products.
You would use the "natrium" number to know how much sodium you're getting.