If you need to translate an application you've created into different languages, then poEdit could be your most convenient and painless solution.
poEdit is a free utility which displays program information in a clear and easy to use format so that you can see what has and hasn't been translated properly instantly. All the different fields are clearly ordered and organized with the name of the item or phrase on the left and the translation on the right. For those that translation you are not happy with, you can mark them as pending and add comments regarding what you think it should mean.
poEdit might not be suitable for translating large applications but it's ideal for those who develop small utilities or plugins and want them to reach the widest audience. The only problem you might find is when trying to delete entries. While editing translations is easy, removing them is a mystery.
If you're a developer needing a simple way to translate your application or plugin, poEdit is an efficient little tool.