Creating a language definition file
From Joomla! Documentation
This page was written for Joomla 
. Joomla 
has slightly different requirements, as explained in Specification of language files. See the PHP documentation for more details.
Important note: Joomla language .ini files must be saved as UTF-8
The format of language definition files is very basic. Blanks lines and lines beginning with “#” are ignored and the latter may be used to add comments to the file. Each line consists of a pair of strings separated by an equals sign like this :
KEY=Value
where “KEY” is a string to be translated and “Value” is the translated string. For example :
ADDITIONAL_INFORMATION="Additional Information"
The “KEY” must be in all capitals or the string will not be found. The case of the source string does not matter as strings are folded to upper case before searching takes place. So “additional information”, “Additional Information” or even “AdDiTiOnAl InFoRmAtIoN” will be matched.
The “KEY” can include spaces and other punctuation characters but there should not be any spaces either side of the equals sign as spaces are significant. If more than one entry has the same left-hand side, the last one to be encountered is the one that will be used.
The "VALUE" cannot include double-quote characters ("). To get a double-quote character you must use the HTML special character sequence """ instead. Single-quote characters (') are valid.
More information about the discussed changes for the Joomla 2.5 and 3.x series can be found on the page Specification of language files