UserControls should be localized in the same way as forms ( Localizable = True , Language = ... ), you do not see localization in the designer when they are embedded in the localized form, but localization works well at runtime.
For the RightToLeft : property, select your UserControl (select the control inside it and press ESC until the main control is selected - in the properties panel you should see the name of your UserControl and type = System.Windows.Forms.UserControl ), go in the properties panel and find the RightToLeft property, in the same panel you also have the Localizable and Language property, which should be used in the same way as in Forms.
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