Can you connect German kitchen appliances that run at 240V to a US stove outlet which is also 240V?

Check the frequency - European appliances run at 50Hz (cycles per second), while US appliances expect 60Hz.

However, this is generally unimportant for things like TVs or stereo equipment. It may be important for anything with a motor, because a lot of these motors run at the mains frequency, and will run too fast if connected to a 60Hz supply.

You would also want to make sure the connections are correct - you will have to re-wire the plug to fit, and it's important to get the live and neutral correct unless it's a double insulated appliance with a non-polarized two prong plug.

It would be wise to make an adapter pigtail with an overcurrent device in it. If it is just a regular kitchen appliance the 50A oven circuit is overkill by a long shot. If something fails the breaker will not blow as it is rated far too high. Making a pigtail with a breaker is simple, and will allow you to not modify anything you already have.