The link fris posted is a great tool, but to actually filter by country (and not simply language) you will require a database and some block / redirect rules.
Keep in mind that neither method is perfect, and if you are looking for something simple, language will suffice.
Anyhell, these two links should get you started if you want to play w/ geoip:
http://www.maxmind.com/app/geoip_country (free database / info)
http://www.maxmind.com/app/mod_geoip (apache api)