When I create a new adgroup through the addAdGroupList function of
Apility the following happens:

Sent UTF-8 valid string: Vêtements femme
Received: string(18) "Vêtements femme"

Does anyone know why calling $adgroupObject->getName() returns a UTF-8
invalid string?

There is a small bug in the shipped version of NuSOAP of APIlity
1.12.0. A line that should have been commented-out is active. Search
for line 614:
$body = utf8_encode($body);
and change it to
// $body = utf8_encode($body);