Yes, I use a similar device for this. Of course, you then test both RJ-45 sockets plus the cabling.
Which power can be transmitted over which distance depends on the wire cross-section and whether the cable is shielded or not. This device is not able to do that. It only tests whether there is a correct connection or whether cables are crossed or short-circuited.
Does the inserted 9V block have the full capacity? When the upper switch is set to "Auto" and the unit is switched on, the LED row from 1 to G runs through. In "Manual" mode, I can manually switch through the signals from 1 to G by pressing the "Test" button once.
I can imagine that a German language setting is not available in this price segment. In any case, I haven't found anything. Otherwise, I would try it via the SETUP button. We use a FLUKE tester where you can change the language.