Nice to see that someone is still maintaining the original GTK1 toolkit. It's like the classic Win32 UI API for the Linux/Unix. Linux UI libraries are a constantly moving target and one can be easily more occupied by adapting to those toolkit API changes instead of focusing on the features of the application itself. I guess that CinePaint developers decided at some point that they don't want to endure API changes in the UI toolkit anymore.
On the other hand, I think GTK1 doesn't even support Unicode.
On the other hand, I think GTK1 doesn't even support Unicode.