I was investigating a bit, under Ubuntu, but I suspect this is quite similar in Debian... will verify a bit more tomorrow.
paul@jacko:/etc/menu$ dpkg -L twm /. [...] /etc/X11/twm/system.twmrc-menu /etc/menu-methods /etc/menu-methods/twm /usr /usr/bin /usr/bin/twm [...] /usr/lib/X11/twm paul@jacko:/etc/menu$ paul@jacko:/etc/menu$ cd /etc/X11/twm/ paul@jacko:/etc/X11/twm$ ls menudefs.hook system.twmrc system.twmrc-menu paul@jacko:/etc/X11/twm$ ls -lh total 16K -rw-r--r-- 1 root root 3,9K jan 27 21:37 menudefs.hook -rw-r--r-- 1 root root 6,6K jan 27 21:37 system.twmrc -rw-r--r-- 1 root root 2,7K sep 6 2018 system.twmrc-menu In system.twmrc there is: menu "/Debian/Applications/Shells" { "Bash" f.exec "x-terminal-emulator -T \"Bash\" -e sh -c \"/bin/bash --login\" &" "Dash" f.exec "x-terminal-emulator -T \"Dash\" -e sh -c \"/bin/dash -i\" &" "Sh" f.exec "x-terminal-emulator -T \"Sh\" -e sh -c \"/bin/sh --login\" &" } paul@jacko:/etc/X11/twm$ whereis x-terminal-emulator x-terminal-emulator: /usr/bin/x-terminal-emulator /usr/share/man/man1/x-terminal-emulator.1.gz paul@jacko:/etc/X11/twm$ file /usr/bin/x-terminal-emulator /usr/bin/x-terminal-emulator: symbolic link to /etc/alternatives/x-terminal-emulator paul@jacko:/etc/X11/twm$ file /etc/alternatives/x-terminal-emulator /etc/alternatives/x-terminal-emulator: symbolic link to /usr/bin/xfce4-terminal.wrapper paul@jacko:/etc/X11/twm$ file /usr/bin/xfce4-terminal.wrapper /usr/bin/xfce4-terminal.wrapper: Perl script text executable paul@jacko:/etc/X11/twm$ cat /usr/bin/xfce4-terminal.wrapper #! /usr/bin/perl -w # # Terminal.wrapper - Debian terminal wrapper script # # Copyright (c) 2004-2005 os-cillation # while ($opt = shift(@ARGV)) { if ($opt eq '-display') { $arg = shift(@ARGV); push(@args, '--default-display', $arg); } elsif ($opt eq '-name') { $arg = shift(@ARGV); } elsif ($opt eq '-n') { $arg = shift(@ARGV); } elsif ($opt eq '-T' || $opt eq '-title') { push(@args, '--title', shift(@ARGV)); } elsif ($opt eq '-geometry') { $arg = shift(@ARGV); push(@args, "--geometry=$arg"); } elsif ($opt eq '-fn') { $arg = shift(@ARGV); } elsif ($opt eq '-fg') { $arg = shift(@ARGV); } elsif ($opt eq '-bg') { $arg = shift(@ARGV); } elsif ($opt eq '-tn') { $arg = shift(@ARGV); } elsif ($opt eq '-e') { $arg = shift(@ARGV); if (@ARGV) { push(@args, '-x', $arg, @ARGV); last; } else { push(@args, '-e', $arg); } last; } elsif ($opt eq '-h' || $opt eq '--help') { push(@args, '--help'); } } exec('xfce4-terminal',@args); paul@jacko:/etc/X11/twm$ paul@jacko:/etc/X11/twm$