[gtkmm] Invalid UTF8 string passed to pango_layout_set_text()

[Francis Bacque <opl opltech net>]

Hello,
when I try to display text (with accent) in a treeview, I can't display
these characters and got repeated messages in the console:
WARNING **: Invalid UTF8 string passed to pango_layout_set_text()
I had tried to convert them with:
Glib::locale_to_utf8 ( const std::string&  opsys_string  ) 
But it didn't succeeded :-(

What' s wrong?

Thanks

Francis