WordPress Translation: How To?

Hi folks,
I'm looking for a way to translate my WordPress site(s) into multiple languages.

In the past I've seen websites with Flags for the different countries/languages that a person can choose. I'm wanting to do something like that on my new (in-development) multisite website.

Are there any reliable WordPress plugins either from WPMU or trusted WordPress apps outside of this site? Or.... is my only option to hard code it in?

Thanks,
Morgan Johnstone