Three simple steps to localize
Depending on your application, you should check legal issues, cultural differences, standards, and more. These issues may result in logical changes to your source code. For example, accounting rules differ between the USA and Germany and popular payment methods vary, too.
Cultural differences can bring you serious trouble or kick your product completely out of the market. I'm sure that you don't want to offend your users.
You should never use certain colors, body parts, or animals. Different cultures see these things differently.
There is a rumor about Borland from the very early days. In Germany, Borland used a pig in the Turbo Pascal ads. These ads were very popular: a pig brings luck and can represent speed in Germany. The rumor is that the Borland founder and former CEO, Philippe Kahn, stopped the German ads. As a native Frenchman, he did not want a pig associated with his products.