Libgda and Libgnomedb are written in C, some bindings for other languages exist:
C++
Murray Cumming and the folks at Openismus are maintaining C++ bindings for Libgda and Libgnomedb.
Tarballs are at http://ftp.gnome.org/pub/gnome/sources/libgdamm and http://ftp.gnome.org/pub/gnome/sources/libgnomedbmm
Source code is also available in the Gnome SVN repository, or at http://svn.gnome.org/viewcvs/gnomemm/libgdamm and http://svn.gnome.org/viewcvs/gnomemm/libgnomedbmm for online browsing.
Python
PyGda (Gda bindings for Python) is part of the gnome-python-extras package. Libgnomedb does not have any python bindings.
C#
Daniel Espinosa maintains C# bindings for Libgda and Libgnomedb, available in the Gnome SVN repository, or at http://svn.gnome.org/viewcvs/libgda/tags/libgda_3_0_before_removing_gda_sharp/gda-sharp or http://svn.gnome.org/viewcvs/libgnomedb/tags/libgnomedb_3_0_before_removing_gnomedb_sharp/gnomedb-sharp for online browsing.