Apologies if this is obvious and I missed it. Does this define a way to store the strings in various languages?

I think this is just the format and specification itself, language selection and file storage and the like will depend on an implementing library. The i18next version for example (bizarrely) puts the whole string in a JSON key, but to be honest I think this is a bad example: https://github.com/i18next/i18next-icu?tab=readme-ov-file#mo...