Translations between languages is quite simple in Magento. For an advanced developer, who has already worked with PHP frameworks, it is not a matter to discuss, but for a beginner it may need a few words of explanation. All texts on the page that should be translated, are stored in CSV files, in /app/locale/[language] directory. The [language] part of the path is build of language code, e. g. 'en_US'.
If you have a look at the files content, you will find that every file structure is the same, one line contains two texts: one in your default language, and one in the destination language. To use the files - also called dictionaries - they must be declared in module's config file (config.xml). You should put this code directly inside your frontend or admin node of the config file.
That's all. Now, when you want to use a phrase that should be translated, use:
Magento will look in you dictionary files for the phrase 'text to translate' and will return the corresponding text in the proper language.