"Created_by" and "Updated_by" can't get localized name.

For a user who has localized name, try to get the record with following code:

var body = {
"app": 556,
"id": 10424
};

kintone.api(kintone.api.url('/k/v1/record', true), 'GET', body, function(resp) {
// success
console.log(resp);
}, function(error) {
// error
console.log(error);
});

You will find "Assignee" and "user_select" is localized name, like this:

value: {code: "lily@abc.com", name: “李丽"}

But "Created_by" and "Updated_by" isn't, like this:

value: {code: "lily@abc.com", name: "Lily Lee"}