I am just listing some Carriers from european Axis powers who might have been in service if their leaders would have decided so, some of them were near completion :
I did look at wiki
Germany :
1. Graf Zeppelin : It was launched in 1938, the carrier itself was near completion but never went operationnal, it was to have 50 aircraft, quite a big carrier.
2. Flugzeugtrager B : The hull itself was completed in 1939 but never launched, like the Graf Zeppelin, it was to have 50 aircraft on it.
3. Seydlitz : constructed as a heavy cruiser, construction was having all sort of delays. In 1942 it was decided to convert it to an aircraft carrier. Never completed.
I will add Italy who did begin production of some too but never went operationnal.
However, it would be nice to have the option of building them if a player want to play an Axis who would decide to put more emphasis on naval power, for what it's worth. For example an Axis wanting to try a Sealion or an Axis just wanting to put more pressure on the Commonwealth's convoys, with a strategy using U-boots, naval-air aircraft, surface ships and aircraft carriers. And possibly not doing a Barbarossa against USSR, or doing a late Barbarossa in 1942, or choosing to play more defensively in the East.
The launch of the German aircraft carrier Graf Zeppelin :
