It's called the Masuda Method. For example, if you have a French game, all of your Pokemon are labeled French. If you breed one of your Pokemon with any other language label (English, Japanese, German, etc.) then your chances of getting a shiny are much higher.
In a 4th gen game, the odds are 4/8192. (1/2048)
In a 5th gen game, the odds are 6/8192. (1/1366)
I can attest to it myself - I bred an english Scrafty with a Japanese Ditto, and the seventh egg was shiny. Obviously that's not going to happen every time, but the odds are much better.