Geany uses the [Scintilla](https://www.scintilla.org/) editing widget which unfortunately states in its documentation "Scintilla provides only limited experimental support on Windows for right-to-left languages like Arabic and Hebrew. While text in these languages may appear correct, interaction with this text may not work correctly as occurs with other editors.".
I would have expected the cursor to jump to the right and go backwards not move LTR in RTL text, so even Gnome editor is not totally correct.
I'm sure contributions to Scintilla would be welcomed.
Closing as its not something Geany can improve until Scintilla is improved.