<?php

$movies = [
    "Indiana Jones et le Royaume du Crâne de Cristal" => ["Harrison Ford","Cate Blanchett","Karen Allen"],
    "Indiana Jones et la Dernière Croisade" => ["Harrison Ford","Sean Connery","Denholm Elliott","John Rhys-Davies"],
    "Indiana Jones et le Temple maudit" => ["Harrison Ford","Kate Capshaw","Jonathan Ke Quan"]
];

    foreach($movies as $key => $value) {
        $msg = "Dans le film $key, les principaux acteurs sont : ";
        for ($i=0; $i<count($value); $i++) {
            $msg .= $value[$i];
            if ($i < count($value) - 1) { $msg .= ", "; } else { $msg .= ".<br>"; };
        }
        echo $msg;
    }