I tried a US DVD and that seems to play fine on Totem.
However, I installed the libdvdcss package and I still seem to be having trouble playing region 2 DVDs. They don't work in Totem and if I try to play them in mpv, it seems to decode some of the CSS keys, but then says 'Failed to recognize file format'. I'll look into it some more later and see if I can figure it out.
