The Localization class allows you to translate your Unity project in different languages.
Just put a localization XML for every language (you want to support) into you resources folder. It'll have many "string"-entries, that you can also structure hierarchically in the XML (e.g. different scenes).
You can then access the localized strings via Localization.Instance.s("localization_key") in your scripts. Of course you can also switch the language via API.
This package contains an example scene and example localization files - this'll give you a quick start!
In the future, an editor interface is planned to manage the localization files.