Hi João, Thanks for the new pictures of the mark. The mark content is as James already said. In addition I have to say that the mark characters look like printing fonts.
龍泉 Dragon Spring by: James
Hey João and Peter,
I enlarged the mark and I think the 2 characters on the right says 龍泉 or Dragon Springs in Chinese. It is place famous for this colored porcelain as well as swords. I agree with Peter that this use of "China" on the left can only mean it is recent.
celadon plate by: peter
Because of the light reflection I cannot read the right two characters in the mark for sure. However, the left two mean China.
Please consider the following two facts. (1) "China" written in Chinese characters wasn't used in Chinese marks until about mid-20th century. (2) The traditional manner of writing is top down, right to left. Here it appears to be top down, left to right. The conclusion that remains is that it cannot be very old and is not an antique.