Userscript implementation because extensions cannot inject remotely hosted scripts like Google's Translate widget script.
Use the Violentmonkey or Tampermonkey menu entries to inject the widget just this time, or to set the script to inject automatically on the site in the future. (If there is a way to do it in Greasemonkey, let me know.)
If you don't get the Google Translate bar, one possible reason would be Content Security Policy (CSP). This is a rule sites can set to control which script sources are allowed for a page. The developer tools Console (F12) may report this issue when it occurs.
I prefer having the bar inserted on every page automatically (or I use Greasemonkey)