@Cask - dont really know of any sites that has the kind of info. Years ago we built these charts, but they became out-dated really fast and with the demise of Yahoo in Europe, we're really only looking at Google - with a pinch of Bing. By far the most most countries are Google territory.
@ Truegho - if you want your site to rank and drive traffic from a local language search, you need to have content in that language. Period.
So to answer your question; yes, you need to translate the content you want to rank for. You can start by taking the most popular/valuable content and then work your way down to corners of the site. General rule is to translate what you want ranked. However you need internal linking structure and site architecture to make it real good though, so you'll often end up with the need to translate a big piece of the site.