Any number of terms in additional languages and dialects can be specified for a given code in the "Designation" field (eg ValueSet.compose.include.concept.designation ) where the particular language refset to be referred to can be mapped from the language code field "Language"(eg ValueSet.compose.include.concept.designation.language) and the type of the term (ie FSN, Synonym, Definition) is held in the "Use" field ValueSet.compose.include.concept.designation.use.
The ExpansionProfile resource can be used to augment information supplied in ValueSet elements on request. Michael Lawley Reuben Daniels - can you help out here? Also suggestion that the ValueSet is not the correct place to making language reference set available. Rather it should be augmented locally in the specific implementation. Suggestion that the display element should specify the language code, but perhaps this is better done in an extension rather than forcing everyone to deal with it (ie core). Also since ValueSets can be defined using filters (ie intesionally) that display terms would not be relevant in this case.
Note that all resources include an inherited "language" field which states the default language for all strings where a language code is not otherwise specified.
TODO: CodeSystem Supplement. Peter Jordan?