Dynamic lang tag

[dachafra]

issue: obtain a language tag for a rdf:langString from a result column

suggestion: "standardize" rrx:languageColumn; use rr:language as fallback for the case when the languageColumn value is null; extend to be able to use templates (eg "{language}-{Script}")

[VladimirAlexiev]

RML has dynamic lang (but no fallback). OBDA and R2RML don't

[dachafra]

Same as I've already commented at #1.

This should be already solved by the extension about Language proposed by @pmaria.
Once the repo/spec will start, we can close it