Thank you for the provided information and steps on how to replicate the behavior of interest.
The behavior that you have shared is actually a simple validation message which comes from the ASP.NET MVC Framework. And more specifically, it comes from the model. Those validation messages could be customized as follows:
"Age is required!!"
The localization of the Kendo UI widgets aims to localize all of the buttons, tooltips, strings within the context of the widget. Since the validation is applied externally, it has to be handled separately.
I hope this helps.
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