The language titles come from .Net framework and are displayed the way they are by default.
There is a workaround to change that, using css (with the css widget). You can select the Language Selector control and change the style of the item you want (and apply capital letter to it).
Another option is using java script widget and jqeury
where you call string.ToUpperCase method of the selected value.
The third option is a custom widget that inherits from LanguageSelectorControl
I hope that helps.
the Telerik team
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