Ivan Pohorilyi,
We have reviewed your query based on the information
provided. As per the default behavior of the Flutter framework, the Ukrainian
language localization does not start with a capital letter. However, you can
override the custom texts in the Flutter Calendar by using the extendibility
options.
To override the custom texts in the Flutter
Calendar, please refer to the following link in our KB documentation: https://www.syncfusion.com/kb/12328/how-to-override-the-localization-in-the-flutter-calendar
You can refer to the link you provided for more
details about the "DateFormat" class in Flutter: https://api.flutter.dev/flutter/intl/DateFormat-class.html.
Please let us know if you have any further concerns.