All audio files in World Of Goo are stored as standard OGG files. However, although it is not used in the original game, it is possible to have different audio files play depending on the language World Of Goo is being played in. Presumably this could be used to translate dialogue into different languages.
When loading an OGG file, World Of Goo also looks for a language-specific alternative. This alternative has the exact same file name as the original OGG file, only with a slightly different extension. The extension consists of the two-letter country code of the language World Of Goo is being played in, followed by a period, followed by the standard "ogg". The file must also be in the same folder as the original OGG file.
So, for example, a file named temp_main.en.ogg in the same directory as temp_main.ogg would play at the main menu when World Of Goo is being played in English. Similarly, renaming the file to temp_main.de.ogg would cause this to play when playing in German.
There are a few rules to keep in mind when using this feature:
This feature does not only apply for OGG files used in the original game; any OGG file loaded by World Of Goo will be overridden if a language-specific alternative exists. That is, whenever the game loads an OGG file through the a level's .resrc.bin file, a ball's resources.xml.bin file, Therefore, this will work in the same way for custom OGG files and custom levels/Goo Balls that load them. This, as mentioned earlier, can be used to, for instance, translate dialogue in a level or total conversion.