Hmm, let’s see if it’s related to cached data at all. First back your project up entirely somewhere safe, then delete the Saved, Intermediate, and DerivedDataCache folders from your project folder. These will regenerate when you launch the project.
Then, launch the project itself and try building the localization data, if it hangs again try and let it run for a while then grab the logs. They might offer some insight to what is processing.
If this is a C++ project, Live Coding has been known to hold some files in processing, blocking the localization tool from accessing them, possible causing issues like this thread: