When localizing RadSpell to e.g., German, buttons' text is longer than expected and overflows outside the button.

To fix the issue you can use an external dialog css file like in this code snippet:

ASP.NET 
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<asp:TextBox ID="textBox2" runat="server" width="100%" Height="100px" 
    TextMode="MultiLine">Dies ist eine Textbox mit ainigen absichtlichen fehlern.</asp:TextBox>
<br />
<telerik:RadSpell ID="spell2" runat="server" ControlToCheck="textBox2" Language="de-DE"
    DictionaryLanguage="de-DE" SpellCheckProvider="EditDistanceProvider" Skin="Silk" DialogsCssFile="spell-dialog-css.css"></telerik:RadSpell>


CSS
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button {
    overflow: hidden;
    white-space: nowrap;
    overflow: hidden;
    -ms-text-overflow: ellipsis;
    -o-text-overflow: ellipsis;
    text-overflow: ellipsis;
}