To add a translation of an article you should prefix the articles title with the language code that your translating to. For example:
- English: en:Main_Page
- Español: es:Main_Page
- Deutsch: de:Main_Page
You should also change the articles title to reflect the language you are translating to. The same basis applies for any articles you are writing that are not translations i.e. writing an article that doesn't exist yet in any particular language should still have the language code attached.
See below examples: