"Now when you’re on your iPhone, your Windows Live friends will be able to see when you’re online, and send and receive messages from them. You can also add new Windows Live friends right from the app.
In addition to supporting Windows Live conversations, we also added more languages in a prior release. Those of you who speak French, German, Italian, and Spanish can enjoy Yahoo! Messenger for iPhone in your native tongue.
If your iPhone is set to one of those four languages, Yahoo! Messenger for iPhone will detect that automatically and load the same language."
To download the new version, tap the App Store icon on your iPhone and search for Yahoo! Messenger (you may also see an update alert on your App Store icon).