xev ouput for the right ALT key:

KeyRelease event, serial 37, synthetic NO, window 0x4000001,
    root 0x170, subw 0x0, time 37556, (96,-15), root:(727,342),
    state 0x80, keycode 108 (keysym 0xfe03, ISO_Level3_Shift), same_screen YES,
    XKeysymToKeycode returns keycode: 92
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False



xev ouput for the left ALT key:

KeyRelease event, serial 37, synthetic NO, window 0x4400001,
    root 0x170, subw 0x0, time 167098, (154,-12), root:(785,345),
    state 0x8, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False


The left ALT key is to do the same as the right ALT key.