Before you can start localization you must make sure that the file or database you want to localize can be localized. This process is called internationalization (Wikipedia). Internationalization of application contains try important parts. The first is resourcing where you replace hard-coded strings with resource strings. The second is code enabling where you make sure that you don't have any single locale or language depent code. Generally you have to follow the internaionalization guidelines set byt the author of the platform you use. For example if you use .NET you should follow the internationalization activles found in MSDN.
Writing properly internationalized code from the start is not any harder or slower than writing staditional locale depent code. This is why you should learn how to write property internationalized code and always write such code. Even if you don't plan to localize you application right now it is better to write internationalized code. If you already have source code that has not been internationalized you can use Soluling's Resourcer tool. It removes hard coded strings from your source code files and replaces them with resource strings.
Use our internationalization API to use more advanced features that the native API of your platform does not provide.