$ xprop -root _XKB_RULES_NAMES_XKB_RULES_NAMES(STRING) = evdev, pc104, us, altgr-intl, I can see that this property on the root window contains five strings. But I found no way with xprop to set it! The tricky part is to set a string array so that it looks like shown above.If xprop cant do it another tool is fine, too.
How to set an X property that is an array of strings?
x11
I found no way with xprop. So I wrote xproperty, which can do that. Its a little Python program on github.