Letting all the overall agenda aside, how does this sound?
js> ds = new RDFSimpleTripleDataStore();
js> em = new RDF.Vocabulary('urn:x-moz:em#');
js> ds.assert(RDF.resources[document.location], em.title,
RDF.getLiteral("Some English string", null, "en-US"));
js> c = ''; ds.forEach(function(t) {c += t;}); c
<about:blank> <urn:x-moz:em#title> "Some English string"@en-US.