Créer 2 fichiers :

logo-switcher.php et logo-switcher.xml

Contenu du fichier PHP :

<?php

defined('_JEXEC') or die;

    $image = $helper->get('logo-fr');
    
?>


<?php if (JFactory::getLanguage()->getTag()=="en-GB"):?>
 
        <a class="" href="/index.php"><img class="sm-logo" src="/<?php echo $helper->get('logo-en'); ?>" alt="<?php echo $helper->get('alt-en'); ?>" /></a>
 
        <?php else: ?>
 
        <a class="" href="/index.php"><img class="sm-logo" src="/<?php echo $helper->get('logo-fr'); ?>" alt="<?php echo $helper->get('alt-fr'); ?>" /></a>
 
<?php endif; ?>

Contenu du fichier XML :

<?xml version="1.0" encoding="utf-8"?>
<form>
    <title>LOGO Switcher</title>
	<sampledata></sampledata>

    <fields name="LOGO Switcher">
        <fieldset name="logo-switcher">
            <field name="logo-en" type="media" default="" label="LOGO-EN" />
            <field name="alt-en" type="text" default="" size="40" label="TEXT_ALTERNATIVE" />

            <field name="logo-fr" type="media" default="" label="LOGO-FR" />
            <field name="alt-fr" type="text" default="" size="40" label="TEXT_ALTERNATIVE" />
            
        </fieldset>
        
      </fields>
      
      
      
      
      
      
</form>

Affiner si necessaire !