Hi Karin, 
This is covered under the Translating the hard-coded text in Squarespace header in on our support page 
You fill find the instructions and appropriate extension file there. 
Cheers
 
 
 

Replace this code in the squarespace extensions file:

if (readCookie('language') != '') {
 currentlanguage=readCookie('language');
 } else {
 currentlanguage = 0;
}

Replace all above lines with this single line:

currentlanguage = 1;

Other than that, translate the text to Swedish in the hard coded extensions file/