Hi Juanito,
I check and I have all dependance loaded but I have the same error.
About mtpaint, I have recompiled it again with the locale specification in the ./configure and I have reinstalled it.
I have the:
gdk-warning, locale not supported by C library
gtk-warning, locale not supported by C library
if language on boot is it,
if I set lang=C I have only the gdk-warning error
Ps.: mtpaint work I had only the warning