Thank you for your question.
RadControls for WindowsPhone don't support Spanish for the moment. So it is expected that you don't see localized string for Spanish. If you change the language to German, French or Italian, you will see the text in the language that is selected. However, we provide a flexible mechanism, which allows you to localize the controls with code or with resource files. More information about localization is available here
If you have other questions, don't hesitate to write us back.
the Telerik team
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