Thanks for the sample. The issue is caused by few of the Editor's ImageBrowser and FilterBrowser messages. It seems that they got incorrectly encoded by the framework. Thus I suggest you to override them in the Editor template similar to the following:
@(Html.Kendo().EditorFor(m => m).Messages(messages => messages
.ImageBrowser(im => im.InvalidFileType(" ").OverwriteFile(" ").DeleteFile(" "))
.FileBrowser(im => im.InvalidFileType(" ").OverwriteFile(" ").DeleteFile(" "))
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