I mean, is it safe? I heard the water in the toilets of the owl of harmful gases into the hole of the bowl entereting avoided. So if ustop water supply, water slowly leaking toilet verschwindet.Meine that as it is prudent to turn it off until I fix the leak?

sure you will be safe. Many people do it all the time here. they shut it off when they go south for the winter, and turn it back on when they return in the spring.
Absolutely. I shut off the main water supply to my house whenever I leave town. I have never had a problem. I believe the primary reason for water in the toilet is to assist in removing the waste and helping it flow through the septic systems.