Constraining searches by language or dialect is a type of constraining by Reference Sets. For every translated version of SNOMED CT, this technique is mandatory. Filtering of search and navigation results to include only those Descriptions that are referenced by the Language Reference Sets may be applied to limit a search to those Descriptions applicable in a particular language or dialect. A single common encoding language should be mandatory in search use cases directly connected to data entry, to avoid confusion and ambiguity. There are a few use cases where a user may legitimately wish to search for Descriptions included in extensions of other countries. For example, when mapping SNOMED CT to other code sets, en-US (American) Descriptions may be required if extensions are not available in the UK language Reference Set.