Apple magic keyboard weird behavior

I'm going to defer to people like @nohillside and @Tom Gewecke for internationalization and keyboard setups, but you can rule out a factory reset of Apple bluetooth devices quite quickly assuming you have a Mac computer you can borrow and pair to the keyboard in question.

1. Enable Bluetooth in the menu bar
2. Hold Shift and Option keys when you click on Bluetooth icon (and you can let go of the modifier keys once the menu is visible).
3. Choose Debug - Factory reset all connected Apple devices or choose the specific device - navigate to the sub menu and choose Factory Reset

I'm guessing this is less than 50% your issue, but if it does - you'll be set (or have fewer items to chase down) and know how to reset Apple Bluetooth devices.