We have all done this. Type the answer, press check and realize you have used the wrong alphabet. Is there any way the system could tell you that you have made a mistake rather than just marking incorrect?
A warning system to notify you that you are using characters that are not present in the language you are studying would be a nice feature.
If you are using the website to study you can install the duokeyboard extension that automatically changes your keyboard input to the language you are using as a workaround to prevent the problem.
After installing start working on a course and you will be asked to enter your settings once it is required. After saving your settings, you will not be asked again for that language. If you want to change your settings later press the extensions button on the top right of your browser or go to the options page through the extensions page of your browser.