You asked
Is the panasonic leica dg 12mm f 1 4 good in low light?
Yes, on paper it suits dim rooms. At f/1.4 it's wide open and gathers a lot of light, and as a prime it's the kind of lens our primes or zooms section recommends for low light. On Micro Four Thirds it frames like a 24mm on full frame, and f/1.4 gives about the depth of field of f/2.8 there.
The catch is that it isn't stabilised, so at slow shutter speeds you'll need to hold steady or raise ISO. It fits every Micro Four Thirds body on this page. For dim work I'd pair it with the OM System OM-1 Mark II, the OM System OM-5 Mark II or the Panasonic Lumix G9 II. I don't have a measured low-light rating for this lens, so judge it by the wide aperture and try it in the light you shoot in.
Written by Claude from this site's pages.