Hello Frank,
Indeed it seems that some of the localization options are missing in the resource file and need to be updated. Here is a list of all available localization properties:
public string OkButtonText { get; set; }
public string RecentColors { get; set; }
public string CustomColor { get; set; }
public string BlankColorText { get; set; }
public string HSVSliderDragText { get; set; }
public string HSBSliderDragText { get; set; }
public string RGBSlidersDragText { get; set; }
public string RGBSlidersDecreaseText { get; set; }
public string RGBSlidersIncreaseText { get; set; }
public string ApplyButtonText { get; set; }
public string HSVTabText { get; set; }
public string HSBTabText { get; set; }
public string RGBSlidersTabText { get; set; }
public string WebPaletteTabText { get; set; }
public string NoColorText { get; set; }
public string CurrentColorText { get; set; }
public string PickColorText { get; set; }
public string CancelButtonText { get; set; }
public string HexInputTitle { get; set; }
Here is the list of missing properties to the existing resource files:

Indeed there seems to be an issue with the ColorPicker reading the localization files even after the missing keys were added. Nevertheless, you can use the attached resource files and the code below to achieve the localization. Please keep in mind that the new keys' values need to be updated/translated
<telerik:RadColorPicker runat="server" Culture="de-DE" PaletteModes="All" ShowIcon="true">
<Localization ApplyButtonText="<%$ Resources:RadColorPicker, ApplyButtonText %>"
CurrentColorText="<%$ Resources:RadColorPicker, CurrentColorText %>"
HSBTabText="<%$ Resources:RadColorPicker, HSBTabText %>"
HSVTabText="<%$ Resources:RadColorPicker, HSVTabText %>"
NoColorText="<%$ Resources:RadColorPicker, NoColorText %>"
PickColorText="<%$ Resources:RadColorPicker, PickColorText %>"
RGBSlidersTabText="<%$ Resources:RadColorPicker, RGBSlidersTabText %>"
WebPaletteTabText="<%$ Resources:RadColorPicker, WebPaletteTabText %>"
BlankColorText="<%$ Resources:RadColorPicker, BlankColorText %>"
HSBSliderDragText="<%$ Resources:RadColorPicker, HSBSliderDragText %>"
HSVSliderDragText="<%$ Resources:RadColorPicker, HSVSliderDragText %>"
RGBSlidersDecreaseText="<%$ Resources:RadColorPicker, RGBSlidersDecreaseText %>"
RGBSlidersDragText="<%$ Resources:RadColorPicker, RGBSlidersDragText %>"
RGBSlidersIncreaseText="<%$ Resources:RadColorPicker, RGBSlidersIncreaseText %>"
OkButtonText="<%$ Resources:RadColorPicker, OkButtonText %>"
RecentColors="<%$ Resources:RadColorPicker, RecentColors %>"
CustomColor="<%$ Resources:RadColorPicker, CustomColor %>"
CancelButtonText="<%$ Resources:RadColorPicker, CancelButtonText %>"
HexInputTitle="<%$ Resources:RadColorPicker, HexInputTitle %>" />
</telerik:RadColorPicker>
I have logged that in our feedback portal where you can subscribe it and get notified when there is any progress on it.
As a token of gratitude for bringing this to our attention, we have updated your Telerik points.
Regards,
Peter Milchev
Progress Telerik
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