NSLocalizedString() not working

I have problem with localization.
I created File.strings resource file with this content:
"product_not_found" = "Product not found";
and when i use
NSLocalizedString("product_not_found")
I get “product_not_found”, but not “Product not found”

File.strings structure

Localization

What am I doing wrong? Thank you in advance

Solved using the filename: Localizable.strings
lol…