I'm so sorry that your ability to communicate has been so impacted.
When it comes to hand gestures, I suggest that you and your caregiver invent your own based on what you can easily remember and what your hands are easily able to do.
Another thing you might do is work with your caregiver to figure out in advance what things you're most likely to communicate, and then write them all down on a piece of paper in such a way that you could point to the thing you want to say instead of speaking. (here is an example below)
If you want to do that in a more technologically sophisticated way, you could download an AAC app for an iPad. AAC stands for augmentative and alternative communication. With these apps you can type or tap words, and then the iPad will say them out loud for you. If you have the energy to type out full words, I would suggest an app like
Verbally, which can speak the words you type in. It's an English app, so I don't know how well it would pronounce German. This is a free app--if you're willing to spend money
Speech Assistant AAC also works for German.
If you're not able to type things out, you can get an app where you just need to tap a single button to say a word or phrase. My favorite (free!) app for this is
SoundingBoard. Instead of text-to-speech, this app lets you record a person's voice. Another similar free app is
LetMeTalk, which works for German.
There are plenty of other apps out there if you have the energy to search, but these might be a good starting point if that's something you're interested in.