The first is that the language of the application is separate from the language of the data. Therefore, while the application language and the data language may be identical, they don't necessarily have to be. When designing a multilingual application, there is a fundamental screen design decision you need to make. For each window in your application, you can create a single window which will then be localized for different languages. Or you can create multiple windows tailored for different languages.
Different languages require more or less space to represent the same idea.
As an example, the equivalent of the English Employee Number in German is Mitarbeiteridentifizierungsnummer. The German equivalent would take up much more space than the English version. Generally, a screen in English can hold more information than a similar screen in German. The advantage of this approach is that if you make a change to your application, you make the change once on a single screen. The disadvantage is that your English users are forced to go through more windows, with areas of empty white space, in order to accommodate languages such as German which require the extra space.