manifest.json

{
  "name": "Google-Translate-it",
  "description": "Adds context menu that, when text is selected, opens up a new tab with the google translation tool.",
  "version": "0.1",
  "permissions": ["contextMenus"],
  "background": {
    "scripts": ["app.js"]
  },
  "manifest_version": 2
}

app.js

chrome.contextMenus.create({"title": "Google-Translate-it", "contexts":["selection"],"onclick": translateIt});
function translateIt(i, t){
	var createProperties = {url: "http://translate.google.com/?q=" + encodeURIComponent(i.selectionText)};
	chrome.tabs.create(createProperties);
}

• Source Code
• Add-on

Yeah, I know, I could have used an anonymous function which would have made it four lines of javascript. The extra line is there for beauty.