In RadGanttView, the drag reorder visual element position indicators ('Before', 'After', and 'Inside') are not translated according to the application's UI culture settings (e.g., German), remaining displayed in English because they are hardcoded in the element's template.
To work this around, create a custom DragReorderTemplate and apply it via the CueTemplateSelector of GanttDragResizeVisualCue. This can be applied via an implicit style defined in App.xaml.
<Style TargetType="telerik:GanttDragResizeVisualCue">
<Setter Property="CueTemplateSelector">
<Setter.Value>
<telerik:GanttDragVisualCueContentTemplateSelector DragTemplate="{StaticResource GanttDragResizeVisualCueTemplate}"
ResizeTemplate="{StaticResource GanttDragResizeVisualCueTemplate}"
CreateDependencyTemplate="{StaticResource GanttCreateDependencyTemplate}"
DragReorderTemplate="{StaticResource CustomGanttDragReorderTemplate}" />
</Setter.Value>
</Setter>
</Style>