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 Locale Codes section.
Leave your feedback on this topic here
If you have questions or need support, please visit the Plesk forum or contact your hosting provider.
The comments below are for feedback on the documentation only. No timely answers or help will be provided.