Extend the locale layer of the country-code library so applications can use normal language tags and ordered…

Extend the locale layer of the country-code library so applications can use normal language tags and ordered…: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). Today locale registration and every lookup require an exact, lower-cased key, so values such as en-US or pt BR do…