$LANGUAGE en
$LANGUAGE tr_TR.UTF-8

The name is a language name: letters, digits and _ . - @. The default is C.

A message takes the $LANGUAGE in effect at its $MESSAGE line, so different messages can have different default languages.

$CHARSET name still parses but gives a deprecation warning: it only ever wrote a comment into the generated code. The text bytes are copied as they are — the file's own encoding is the texts' encoding.

Semantics: Reference › $LANGUAGE.