make sure literal lang-tags are valid, re #266
make sure literal lang-tags are valid, re #266

ssssam/rdflib,marma/rdflib,avorio/rdflib,ssssam/rdflib,dbs/rdflib,avorio/rdflib,ssssam/rdflib,avorio/rdflib,dbs/rdflib,marma/rdflib,yingerj/rdflib,marma/rdflib,RDFLib/rdflib,armandobs14/rdflib,marma/rdflib,RDFLib/rdflib,armandobs14/rdflib,ssssam/rdflib,dbs/rdflib,yingerj/rdflib,armandobs14/rdflib,dbs/rdflib,RDFLib/rdflib,yingerj/rdflib,armandobs14/rdflib,yingerj/rdflib,avorio/rdflib,RDFLib/rdflib