Linux

This should work on virtually all Linux machines and probably most *nix
    machines as well, but should be tested before enabling by using the C<LANG>
    environmental variable.  On many Linux systems, the C<LANGUAGE> variable is
    also set, which has a colon delimited set of languages in preferred order.

Linux tends to use a POSIX language tag.  Guidelines for converting these
    can be found in Intl::LanguageTag::POSIX, but should be self contained
    here to avoid providing excess information (like encoding) that a
    LanguageTag::POSIX.new(…).bcp-47 conversion would include.  This work
    will be done for a future version.