Unfortunately to add a new string to the Localizable file, it has to be done manually.
14 must knows for an iOS developer
Norberto Gil Vasconcelos

I just want to add on the Localizable Strings section that your sentence quoted above is not entirely true. There’s a tool called BartyCrouch which solves this problem (both for Code files and XIBs/Storyboards): https://github.com/Flinesoft/BartyCrouch

I hope this helps some people out there.