All the files that are in the lang/1 directory you need to copy these in to a new directory and you need to convert them in to whatever language you are want then repeat the whole process for every other language that your wanting.
Then in the usercp.php file find the below and add your other language options.
Code:
//==Language
$HTMLOUT.= tr($lang['usercp_language'], "<select name='language'>
<option value='1'".($CURUSER['language'] == '1' ? " selected='selected'" : "").">En</option>
<option value='2'".($CURUSER['language'] == '2' ? " selected='selected'" : "").">Dk</option>
</select>", $CURUSER['language']);