To use graphic icons (i.e. flags) instead of a text menu in client area to allow the user the select preferred languages, for each supported language insert in header.tpl where appropriate a line of code as:
<a href="{$smarty.server.PHP_SELF}?language=English" style ="padding-left: 0px !important; padding-right: 0px !important;"><img src="templates/{$template}/images/gb.jpg" title="English" alt="English" width="31" height="21" border="0" /></a>
A wide and comprehensive collection of free flag icons (various styles, formats and dimensions) is available here: https://www.countryflags.com