Unfortunately, no idea. In the search field in the toolbar you can try to change the input method by right-clicking into the text field and use the "Input methods" sub menu, just to try if it makes any difference.
What interface language does Geany use? Maybe it helps to change it to English (if not already set) with the .bat file as described in https://www.geany.org/Documentation/FAQ#QQuestions11. I don't know if there is a direct relation between the interface language and the input methods but it might be worth a try.