Since there is still no answer from the real experts, I will try to play one
The straight blade, small ears and the niello decoration are typical for the early yataghans from the 18th century. You may find similar examples in the Astvatsaturyn's book.
I have also a similar one, which bears the date 1182 (1768) on the both sides. Please notice a top quality hamon (bright and having a uniform width), which you may expect from a Japanese master smith