The coin dropped
Thank you for insisting on creating a "VIEW". You meant it litterally. This I did not understand.
Yes, I think this is the best solution
CREATE VIEW categories_description_v AS SELECT categories_id, language_id, CONCAT(categories_id, language_id) AS mainkey, categories_name FROM categories_description;
I guess, thats what you had in mind.
And it works without hacking DA's extension. Still, as a suggestion: do include it in a further update because some servers don't allow creating views.
Thanks again for your assistance!