Bonds and the yields that an investor gets from them are impacted by risk factors associated with those bonds. This is why the savviest investors look to foreign bonds as part of their portfolio. The foreign bonds allow them to diversify their portfolio and make the greatest return while at the same time minimizing the risk associated.  
International bonds come from companies overseas that need to raise money for some reason. Most companies in the world find themselves in need of capital at some point, and plenty of them turn to the public markets to get the capital they require. The fact that US investors might decide to buy some foreign bonds just make sense.  
Right now, the rates that one can get from US Treasury Bonds is not all that impressive. There are a lot of better rates out in the world of foreign bonds. The world is currently very unstable with a lot going on all at the same time. It is pretty advisable to try to grab some investments that can pay out some guaranteed rates during these questioning times. Bonds from overseas can be the perfect solution to the problem.  
The best thing to do at any time with a portfolio is to keep it diversified. This allows it to withstand the ups and downs of any market condition. The most successful investors have always spread their money out throughout the world. Bonds from another country are a key element to making it happen for the average US investor.