Is it possible to find out that users are translating your site using the browser’s built-in translator? Easy.

Add a Custom html tag with the following content:

    document.addEventListener('DOMSubtreeModified', function(e) {
        if (( == 'HTML') &&
            ('translated'))) {
                    'event': 'UAevent',
                    'eventCategory': 'Behaviour',
                    'eventAction': 'Google Translate',
                    'eventLabel': '{{Page URL}}',
                    'eventValue': null
    }, true);

And in Universal Analytics, events will appear in the events section Behavior > Google Translate > Page URL.