Sets the language filter. It supports a language code (complying to ISO 639-1 code) and optionally a region code (complying to ISO 3166-1).
When using both language and region codes, they have to be written together. AFS also supports usual syntaxes splitting codes using "-" or "_":
afs:lang=isoCode is a shortcut for adding the filter afs:lang="isoCode" to the query. It will be rewritten into afs:filter=afs:lang="isoCode".