VXML, does it speak many tongues?

According to the VXML 2.0 spec the grammar tag has the attribute xml:lang. The spec describes this attribute as "The language identifier of the grammar". Does this mean I can have an English document with a Spanish grammar? I'm not sure, but the description is vague! Why else would the xml:lang attribute exist if this is not the case. But anyway I haven't come to my point yet. If the grammar tag has an xml:lang attribute, why doesn't the field tag? Does this mean I can only have fields in the language of the document? Since many fields are just built-in grammars (e.g. boolean, date) shouldn't it make sense that the attributes match?

Much of this depends on the first point being true, but can you imagine having a VXML document that starts in English but upon recipient request becomes Spanish ("press 1 to continue in Spanish"). Thus all future grammars are Spanish (using xml:lang="es-MX" or something like that). Now we need to grab a date. Does this mean we have to jump to a new document with Spanish as the default language?

Very messy indeed.