How to create a muli-language system

I want to create a multilanguage app, My app will be extensible, with extensions created by users,

But for translation, I don't really know how to do it, I've already seen something like this

English	French
Export Data	Exporter les données
Create a new Game	Créer une nouvelle partie
Change game name	Changer le nom de partie
...	...

Basically, every word or sentence is in a file with it's equivalent in another language

So : Is there any other way to achieve such a system ? And, if the one i presented is the best how to do it ? In which format ? how to differentiate a language from another, and how to differentiate a word or sentence from another

Thanks :)