Plesk locale and language pack names follow the RFC 1766 standard in the format "<languagecode2>-<country/regioncode2>", where <languagecode2> is a lower-case two-letter code derived from ISO 639-1 and <country/regioncode2> is an upper-case two-letter code derived from ISO 3166. For example, U.S. English locale is named "en-US". To see list of locale names supported by Plesk, refer to the Appendix. Locale Code. section.