In the mentioned case, the following turned out: As soon as the module is installed, the translation is also there. It was installed in the test store and was therefore automatically translated. It was not installed in the live store. After the installation in the live store, the translation came immediately.
But now I made another interesting discovery. The module "Block-contact" was installed in the test store (complete new tb installation) with version 2.0.2 and translated from the beginning in German. An update was available, after update it is again in English, just like in the live store (both have now Version 2.0.3).
I do not know if this should be so or not, in any case my original statement/question is no longer correct