Hello there Christian,
This is what worked for me to get the faker locale working in the test script:
window = {};
pm.sendRequest("https://cdnjs.cloudflare.com/ajax/libs/Faker/3.1.0/faker.min.js", (error, response) => {
var text = response.text();
(new Function(text))();
window.faker.locale = "de";
var name = window.faker.name.findName();
console.log(name);
pm.globals.set("name", name);
})