(Click to enlarge)

Thanks for pointing it out way, but...

This kind of thing is the browser's responsibility, rather than each website reimplementing it.

Besides, it is a can of worms. For example, making it always in English is rather imperialistic, but making it translatable would be burdensome. Real sites may also have other warnings there that scroll past it.

Another problem is it simply is not effective. You can run JavaScript in the address bar, and there's no way to put any kind of warning there.
You can try it yourself...
javascript:alert(document.cookie);

Fair enough, though the Composr info at the top of source files isn't translatable either. Just seemed like a simplistic extra security measure. I believe you are correct with the javascript in the address bar, but your example did nothing in Firefox except reload the page.