When modifyOtherKeys is set to mode 2 in xterm, pressing the Alt key in combination with letters on a non-Latin keyboard layout does not produce any escape sequences or characters. This makes it impossible to bind these key combinations to specific actions within applications running inside xterm.
Expected behavior: When modifyOtherKeys-specific sequence cannot be generated, it should send an escape character followed by the corresponding Unicode character, mirroring the behavior observed when modifyOtherKeys is disabled (mode 0).
Current behavior: No escape sequence or character is sent when Alt is combined with letters in non-Latin keyboard layouts if modifyOtherKeys is set to 2.
Steps to reproduce:
Configure a non-Latin keyboard layout (e.g., Russian, Greek, etc.).
Start xterm with modifyOtherKeys set to 2 (either through a resource file or command-line option).
Run showkey -a, press Alt in combination with various non-Latin letters.
Observe that no escape sequences or characters are output.
This issue hinders the usability of xterm with non-Latin keyboard layouts when custom keybindings relying on Alt key combinations are desired (like in far2l project in which I contribute code from time to time). A fix would greatly improve accessibility and allow users to fully leverage their keyboard's capabilities within xterm.
FYI, releated issue in far2l issue tracker
https://github.com/elfmz/far2l/issues/2628#issuecomment-2591151386