Returns a Range object that represents the current region. The current region is a range bounded by any combination of blank rows and blank columns. If we want to be consistent with MS Excel we should implement this property. It is useful for many operations of a region such as filtering(selecting one cell and executing the Filter command should apply it to the current region), sorting, selecting all and etc. This document will be useful: https://docs.microsoft.com/en-us/office/vba/api/excel.range.currentregion.

The operating system region and language needs to be set to Japanese.

RichTextBox seems to have several issues with Japanese, but being locked from visibility or edit is the biggest one.

To recreate, start typing in Japanese, push the "right" arrow after selecting the IME option desired, then hit "spacebar." This seems to duplicate the text, then when trying to continue to type into the text field the text is no longer visible (yet the IME does display).

The native WPF RichTextBox has no issues (and also supports partial selection, etc.).

I've attached a video to show the behavior with 2025 Q1 telerik.

*note:* This is on a machine with NVIDIA graphics. I mention this as there may be some issues with RichTextBox and the hardware... When I'm in a virtual machine with a completely Japanese environment and virtual graphics driver, there is NO text visible at all when trying to type into the RichTextBox. Works fine with other controls and wpf RichTextBox.

When the TitleBarVisibility is Collapsed, the backstage close button is aligned with the top of the backstage adorner. The button should have a top margin applied. 
This reproduces when the BackstagePosition property of RadRibbonBackstage is set to Office2013, which is the default setting of newer Telerik themes.

To work this around, get the backstage close button and set its top margin.

 private void RadRibbonBackstage_Loaded(object sender, RoutedEventArgs e)
 {
     var backstage = (RadRibbonBackstage)sender;
     var closeButton = backstage.FindChildByType<RadRibbonButton>();
     closeButton.Margin = new Thickness(closeButton.Margin.Left, 15, closeButton.Margin.Right, closeButton.Margin.Bottom);
 }

NullReferenceException is thrown when the RadVirtualKeyboard control gets loaded, but it is not added to the visual tree. This skips the initialization of an internal collection which is used on Loaded, thus throwing the error.

To work this around, you can manually call the OnApplyTemplate method of RadVirtualKeyboard before it gets loaded.

virtualKeyboard.OnApplyTemplate();

When RadRichTextBox for WPF is hosted in a WinForms application (through ElementHost), typing with Japanese IME duplicates the typed letters, which makes the control unusable with the default behavior.

Possible workaround: Create custom caret. There are some suggestions in this forum thread: https://www.telerik.com/forums/richtextbox-doesn't-support-japanese-ime-when-hosted-in-winforms