Our customers are located in Russian and CIS. So, the most common language is Russian. Telerik WinForms controls doesn't provide official Russian localization. Yeah, we can translate it, but it's too hard to contact with translators and support them in translation questions. And, of course, it takes money resources. We'd rather pay more monay for Telerik WinForms UI with official Russian localization than we spend money to translators. Thanks!
Here is also something you might find useful for translating strings: https://www.microsoft.com/language/en-us/default.aspx
Hello, for the time being, we do not intend to provide localization strings for languages. What we have is a section, where our users are submitting their localization providers translated into different languages. If you consider this useful, once you translate your app, feel free to do that: http://www.telerik.com/support/code-library/winforms/localization-providers