Optional. The desired language, consisting of an ISO 639-1 language code and an ISO 3166-1 alpha-2 country code, joined by an underscore. For example: es_MX, meaning "Spanish (Mexico)". Provide this parameter if you want the category strings returned in a particular language. Note that, if locale is not supplied, or if the specified language is not available, the category strings returned will be in the Spotify default language (American English). The locale parameter, combined with the country parameter, may give odd results if not carefully matched. For example country=SE&locale=de_DE will return a list of categories relevant to Sweden but as German language strings.