jQuery Grid Plugin - jqGrid

I have a site that is setting CurrentCulture and CurrentUICulture to a language selected by the user.  The code I am using for Spanish is 'es' or 'es-ES'.  However, there is not a grid.locale-es.js file, but instead, a grid.locale-sp.js. 

From information on the CultureInfo Class, "...The .NET CultureInfo class specifies a unique name for each culture, based on RFC 4646 (Windows Vista and later). The name is a combination of an ISO 639 two-letter lowercase culture code associated with a language and an ISO 3166 two-letter uppercase subculture code associated with a country or region..."

On this page, it referenes a codes table, where es-ES is Spanish (Spain): http://msdn.microsoft.com/en-u..... (and es-whatever, is Spanish-whatever).  SP is not considered Spanish.

Is there a specific reason 'sp' was chosen for Spanish for this resource file instead of 'es'?

Thanks,