create/skeletons: Fix languageCode region subtag

[CyrusYip]

Region subtag should be in ALLCAPS

[CLAassistant]

All committers have signed the CLA.

[CyrusYip]

Reference:

• Region subtag

  Optional. This subtag defines a dialect of the base language from a particular location, and is either 2 letters in ALLCAPS matching a country code, or 3 numbers matching a non-country area. For example, es-ES is for Spanish as spoken in Spain, and es-013 is Spanish as spoken in Central America. "International Spanish" would just be es. —lang - HTML: HyperText Markup Language | MDN

[github-actions[bot]]

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