Hi Jenny,
Follow the above steps, that will sort it.
1) Download the file atelier.pot
from wp-content/themes/atelier/languages/
.
2) Re-save that as sv_SE.po
and add your own translations.
3) Then within PoEdit compile a new .mo
file (File => Save as) and upload both of those via FTP to wp-content/themes/atelier/languages/
or ideally your child theme.