wp-catalogue not working with mqtranslate

Hi, I have a problem with wp-catalogue, the translations (eng-ita) don’t work.
Flags add a string (?lang=en) at the end of the url, but the language doesn’t change.
Can you help me please?
This is the gallery link: http://www.sinapsitech.it/prodotti/

https://wordpress.org/plugins/wp-catalogue/