[Richard Suchenwirth] - Writing direction in some writing systems, notably Arab and Hebrew, goes from right to left. With little effort, a Tcl entry widget can be massaged to assume that behavior:

 proc rentry {w args} {
     bind rentry <Key> {
       if [string length %A] {%W icursor [expr [%W index insert]-1]}
     }
     eval entry $w -justify right $args
     bindtags $w [list $w Entry rentry . all]
 }
 # example usage: rentry .e -background grey -textvar foo ...
  
The characters you type in are appended at the left, because the cursor is moved one to the left after the character has been inserted. For decent Arabic or Hebrew entry, the keysyms coming in at %A must of course be mapped to the ''real'' characters they use.

Another approach would be an additional binding to Entry that moves the cursor if justification is "right":
 bind Entry <Key> {+
    if {[string length %A] && [%W cget -justify]=="right"} {
	    %W icursor [expr [%W index insert]-1]}
 }
This way one would not need a new proc. Writing direction of an entry would depend on the selected justification.

I'm just not sure whether right-justification may be "justified" for numeric entry widgets, without wanting a reversal in writing direction...
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See also [A simple Arabic renderer] - [Heblish] - [The Lish family]
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[Arts and crafts of Tcl-Tk programming]