Some parts are imported but it‘s probably as European as possible at the moment. Details about production can be found here: https://www.nager-it.de/en/maus/fertigung. Unfortunately their shop seem to be only accessible in German.
credit: https://www.reddit.com/r/BuyFromEU/comments/1ngg5r6/fair_and_european_computer_mouse/
Not quite from what I can gather. Supposedly the working conditions of the companies/ trading partners are rated (according to the principles listed under https://www.nager-it.de/en/maus/umsetzung/details).