“en” and “en”^^xsd:string are not equivalent on the database system at https://databus.dbpedia.org/repo/sparql which violates the RDF 1.1 spec and thus breaks applications based on contemporary RDF frameworks.
For a detailed record of my findings, please see:
Conclusion: For Jena 3.12.0, “en” and “en”^^xsd:string are indistinguishable - so Databus should fix the string literals to not include an “xsd:string” component - which is the way DBpedia does it.
I think you misunderstood: What I intended to say is: For practical reasons, because your Virtuoso does NOT adhere to RDF1.1, you should mitigate the issue by e.g. either (a) use string literals without xsd:string or (b) use a different (version of the) DBMS
The spec states, that “foo” and “foo”^^xsd:string are synonyms.
(More precise: ALL literals have datatypes, but serializations may allow to omit xsd:string)
Please note that concrete syntaxes MAY support simple literals consisting of only a lexical form without any datatype IRI or language tag. Simple literals are syntactic sugar for abstract syntax literals with the datatype IRI http://www.w3.org/2001/XMLSchema#string .