I'm sorry, I'm not sure I follow! I'm rapidly approaching the limits of my familiarity with Calibre now.
Are you saying I should use the part of the Metadata Plugboard where you can enter code? Would you be able to point me in the direction of the correct code to try?
(I think you're saying to make it so that 'author sort' also incorporates whichever language is in the metadata? Or am I wrong about that? I don't fully understand what you're advising)