RDF literals: "Plain literals have a lexical form and optionally a language tag as defined by [RFC-3066], normalized to lowercase.
Typed literals have a lexical form and a datatype URI being an RDF URI reference."
Why isn't xml:lang information represented within the RDF data model? "The WG subsequently resolved that typed literals would not have a language tag."
Interpretation properties "...they express the relationship between one value and that value interpreted (or processed in the imagination) in a specific way."
Fwd: Typed literals in RDF: "On Friday RDF Core changed the definition of a literal, so that a literal can be one of the following:
A lexical form
A lexical form paired with a language tag
A lexical form paired with a datatype URI"
This is old news (over a year).