Switch language in menu bar

hey there! i`m new to this plugin and also not an expert in wordpress – so i hope you could help me. i installed ztranslate. the managing of the two languages works fine and when i put the ?lang=en oder ?lang=de in my browser, i get the selected language. but how do i make it that i can select the language in my menu bar or on each site in the frontend??? thanks for your help!!!

https://wordpress.org/plugins/ztranslate/