Gboard's autocorrect is not available in German I recently switched to Gboard because of its multilanguage support, etc.

Now I've run into the problem that for some reason, German autocorrection/prediction and the swipe-type feature are missing. Only when I swap to the English keyboard do I get predictions.

Maybe some kind of dictionary is missing?

I am using an updated Samsung Galaxy S7. Primary system language is set to English with German lower on the priority list.
When adding a new language to Gboard for the first time, it may show a notification "Updating your typing experience", possibly for downloading/updating the relevant dictionary.

If it didn't happen, try removing and re-adding the problematic language's keyboards.

In the worst case, you may need to reset Gboard's data by clearing their app's data (generally from the phone's Settings - Apps)