You can localize the following
a) Menus, buttons, navigation links, labels, error messages
b) Business data columns (metadata)
c) Lookup data
d) Task actions
For the business data as such, you cannot localize dynamically. It will show whatever that's in the database. Only exception is the lookup dropdown values which can be localized.
You can add additional language that's not already there. In order to do so, you need to create message bundle properties for every additional language.
Follow the documentation stated below,
There's also a resource kit utility which is referred to in the above article, to help you with the localization.