/usr/share/GNUstep/GNUMail.app/Resources/ is in gnumail.app-common 1.2.2-1.1+deb9u1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/GNUstep/GNUMail.app/Resources/Arabic.lproj/
/usr/share/GNUstep/GNUMail.app/Resources/Arabic.lproj/Localizable.strings
/usr/share/GNUstep/GNUMail.app/Resources/Czech.lproj/
/usr/share/GNUstep/GNUMail.app/Resources/Czech.lproj/Localizable.strings
/usr/share/GNUstep/GNUMail.app/Resources/English.lproj/
/usr/share/GNUstep/GNUMail.app/Resources/English.lproj/Localizable.strings
/usr/share/GNUstep/GNUMail.app/Resources/French.lproj/
/usr/share/GNUstep/GNUMail.app/Resources/French.lproj/Localizable.strings
/usr/share/GNUstep/GNUMail.app/Resources/German.lproj/
/usr/share/GNUstep/GNUMail.app/Resources/German.lproj/Localizable.strings
/usr/share/GNUstep/GNUMail.app/Resources/Russian.lproj/
/usr/share/GNUstep/GNUMail.app/Resources/Russian.lproj/Localizable.strings
/usr/share/GNUstep/GNUMail.app/Resources/Spanish.lproj/
/usr/share/GNUstep/GNUMail.app/Resources/Spanish.lproj/Localizable.strings
/usr/share/GNUstep/GNUMail.app/Resources/Swedish.lproj/
/usr/share/GNUstep/GNUMail.app/Resources/Swedish.lproj/Localizable.strings
/usr/share/GNUstep/GNUMail.app/Resources/Turkish.lproj/
/usr/share/GNUstep/GNUMail.app/Resources/Turkish.lproj/Localizable.strings