From Joomla! Documentation
Jtext method returns the length of the resultant string and outputs the translation. Based on the selected language file above text will change. You can find Language files at /administrator/language/yourlanguage for the backend and /language/yourlanguage for the frontend. suppose your template file contains the english text “Hello” which needs to be made translatable. <?php echo 'Hello '; ?> Then you need replace the static string like this <?php echo JText::_( 'MY_EXT_HELLO' ); ?> This will cause the translation system to search language file for “HELLO”. This is case-insensitive. If the language definition finds string is encountered MY_EXT_HELLO=Hello
If the user changed language file to latin, the output will "Lorem". If the appropriate string does not appear in the latin language file, then Joomla sends the string “Hello” as it is. You can read more here http://docs.joomla.org/Making_templates_translatable.