Gloriosa B made by Haid & Neu and Pfaff B (or type B) have very similar needle plate and bobbin plate to your machine. I have seen the same pattern you have on the face plate on Older Pfaffs (face plate and stop motion screw), as late as on a Pfaff 30 or 31. Yours are older, the large hand wheel makes me think it's pre WWI but hard to tell. Singer's model 12 was a starting point for a lot of machines made in Germany, and ongoing developments were made for decades by several brands. I'm guessing Köhler was one of them too. With a bit of search I'm sure the model will be tracked down.