Plugin settings per site / locale (Craft 3)
There is no native support for this, you can follow my approach and create a custom table for it to store the settings for each site

Another way is to return a different array depending on the current site in your config file

if(Craft::$app-&gt;getSites()-&gt;getCurrentSite()-&gt;handle === X){
    return ['flagName' =&gt; 'Tricolore'];
} else {
    return ['flagName' =&gt; 'Bundesflagge'];
}


or

$array = [
    'de' =&gt; [
        'flagName' =&gt; 'Bundesflagge'
    ],
    'fr' =&gt; [
        'flagName' =&gt; 'Tricolore'
    ]
];

return $array[Craft::$app-&gt;getSites()-&gt;getCurrentSite()-&gt;handle];