We are change the model in v4.0, which is currently a Technical Preview. Once this v4.0 work is completed, it will allow enablement the Shared project. As such, the shared project will have its own set of XLF files, eliminating the duplication of the XLF files.Mark WH commented
I see the exact same behavior as Kevin. The menu item is grayed out for Universal Apps, but enabled for Portable class libraries and full windows apps. I am running VS2015 Professional.