On Linux/Unix, following environment variables can be used to override compiled-in installation paths (MS Windows version always looks to directories relative to path where it was installed). Note they are intended to override system installation paths therefore they are not path lists, they can contain only a single path.
GWYDDION_DATADIR
Base data directory where resources (color gradients, OpenGL materials, …) were
installed. Gwyddion looks into its gwyddion subdirectory for
resources.
When it is unset, it defaults to compiled-in value of ${datadir}
which is usually /usr/local/share.
GWYDDION_LIBDIR
Base library directory where modules were installed. Gwyddion looks into its
gwyddion/modules subdirectory for modules.
When it is unset, it defaults to compiled-in value of ${libdir}
which is usually /usr/local/lib.
GWYDDION_LIBEXECDIR
Base lib-exec directory where plug-ins were installed. Gwyddion looks into its
gwyddion/plugins subdirectory for plug-ins.
When it is unset, it defaults to compiled-in value of ${libexecdir}
which is usually /usr/local/libexec.
GWYDDION_LOCALEDIR
Locale data directory where message catalogs (translations) were installed.
When it is unset, it defaults to compiled-in value of
${datadir}/locale which is usually
/usr/local/share/locale.