* 3-letter ISO code, UNM.49 numeric code, or other valid Unicode Region Code as defined by the LDML specification.
* The identifier will be canonicalized internally using the supplemental metadata as defined in the CLDR.
* If the region code is NULL or not recognized, the appropriate error code will be set ( U_ILLEGAL_ARGUMENT_ERROR )
* 3-letter ISO code, UNM.49 numeric code, or other valid Unicode Region Code as defined by the LDML specification.
* The identifier will be canonicalized internally using the supplemental metadata as defined in the CLDR.
* If the region code is NULL or not recognized, the appropriate error code will be set ( U_ILLEGAL_ARGUMENT_ERROR )