Introduction to template translation
From Joomla! Documentation
Joomla! is a truly international application and supports the translation of all strings contained within it. Templates are no exception, and a little extra time spent ensuring that the strings used in your templates are translatable will pay dividends.
The language translation system has been designed to be as simple and error-proof as possible. For example, even if a language file is missing, or a particular string has not been translated, Joomla will transparently fall back to showing the untranslated string. There are also some useful tools built into Joomla itself to assist translators in creating a new translation.
In this document you will learn about constructing language definition files for your template and how to include translations in your template package file. You will also learn how to make sure that all strings used in your template are translatable and how to debug a new translation.