https://bugs.winehq.org/show_bug.cgi?id=38779
--- Comment #2 from Piotr Caban piotr.caban@gmail.com --- I've sent a patch that improves setlocale speed little. Could you please give it a try?
(It was committed as e9eec98d5c74fb816ee4615d437aefb0d336de92). I'm still planning to optimize the function more when I have time.