Hello stupot, I think your animals will be just fine in your garage temperature wise. This is one of those questions I enjoy researching when I acquire new salamandra subspecies I'm not familiar with. I'd find out where they occur using a distribution map and then look up some of the towns to find out their climate and extremes of temperature. This would give me confidence in how I maintain the animals here in the UK.
In general, continental Europe has lower temperatures than the UK and whilst I know salamanders do not like high temperatures, it is the lower negative temperatures which have always concerned me most. I keep all of my adult salamandra subspecies out side as much as possible moving them into a frost free garage only when temperatures are negative or into the shade, garage when too warm.
These animals have a winter terrarium with a twelve inch depth of leaf mould covering a series of tunnels which lead to the lowest part of the enclosure where I have created a cavern large enough to accommodate several animals. They head there when temperatures get to about 8C. I will also place a thick old hessian sack over the enclosure too. They emerge on milder evenings to feed throughout the winter and whilst they may remain in their burrows for several days, they don't hibernate.
In addition to the temperature, I also look at the monthly rainfall record for each location and the expected type of habitat eg is it forested etc.
Please take a look at this web site. They have a link to a distribution map. Wikipedia will have monthly temperature and rain fall guides you may consult.
AmphibiaWeb - Salamandra atra
