flutter pub get needs to be run in flutter/dev/tools for the generator to work. Another alternative is to run flutter update-packages`. However, this step shouldn't be necessary.

The reason this is happening is because the current localizations script is just a package in the SDK, which is why it requires a pub get call since its dependencies change between flutter versions.

I'm looking into seeing if I can move the gen_l10n tool into flutter_tools so that it does not require re-caching and updating its dependencies.