The lang option defines the language whose collating conventions are to be used. The default depends on the processing environment. Its value must be a valid language code (e.g. en-EN).
To specify what a “valid language code” actually is, it might be helpful to new users to refer to a specific standard document (e.g. ISO, RFC).
At the description of the
langoption ofp:text-sort, there is written:To specify what a “valid language code” actually is, it might be helpful to new users to refer to a specific standard document (e.g. ISO, RFC).