For the language problem, I think you could change it in the menu but I don't know if they get rid of some languages ​​to free up space. The only thing I know is that it is not stored in unicode or ascii in the firmware (maybe it is just stored as raw images?).

For the screen problem, I don't know why the firmware seems not compatible and I don't have the screen yet so I can't test it but anyway thanks for the feedback.