This is the ValueSet that contains all the codes in Language Proficiency VS (http://hl7.org/fhir/us/davinci-pdex-plan-net/ValueSet/LanguageProficiencyVS) and Language Proficiency VS (http://hl7.org/fhir/us/davinci-pdex-plan-net/ValueSet/LanguageProficiencyVS). E.g. what you have to deal with if you get resources containing codes in either of them