Xcode 14 added support for this.
However, in case this helps anyone else, one detail I didn't realize at first is that you have to add the defaultLocalization: to your Package() initializer in your Package.swift file. Otherwise, it doesn't think your package is localizable, and skips it.
let package = Package(
name: "MyLocalPakcages",
defaultLocalization: "en",
platforms: [
.iOS(.v15),
[…]
And then, in Xcode 14, the export fails because by default it tries to build with an old macOS SDK, which doesn't know about all the new SwiftUI stuff. So I had to add this to my Package.swift file too:
platforms: [
.iOS(.v15), // or whatever you might have
.macOS("99.0"), // <-- This is the important part to get it to not build with the old macOS SDK
],