If you read the roadmap you can see that we plan localization for 0.2.
On this project at the moment, the only version we have released is in English. This is because the project is not ready yet to be translated.
The main issue is that messages that are in libpurple are translated with gettext and messages that are in the UI are translated like any other Mozilla-based application. If you try to make your own translation pack, we would be surprised if you managed to get the messages of connection errors in the Account Manager in your own language. And this is only an example...
So we wait for this issue to be resolved before we give translated versions for download. We prefer offering a fully translated version or don't claim it is translated at all.
If you want to help, please wait for the 0.2. We will be happy to have a big community to help us making Instantbird more international.