We do not have the js file for the “Cyryllic” which is must for the translation of calendar. Also when we searched for the code of Cyryllic language for translation, we were unable to find.
You need to add the js file inside the js > lib >chartjs >datepicker > i18n to make them work.
For example you can see in the screenshot below:
So if you could provide the js code by translating into the language your require as given in the sample below then we can help you.
Do not forget to provide the site access in the email given below if you provide the JS code.