Hi Rodrigo,

You can either change the text of the panel manually when the language is changed, or you can create a descendant control with Localizable property for the header text:

  [ToolboxItem(true)]
    class MyCollapsiblePanel : RadCollapsiblePanel
    {
        [DefaultValue("")]
        [Localizable(true)]
        public new string HeaderText
        {
            get { return this.CollapsiblePanelElement.HeaderText; }
            set { this.CollapsiblePanelElement.HeaderText = value; }
        }
        
        public override string ThemeClassName
        {
            get
            {
                return typeof(RadCollapsiblePanel).FullName;
            }
            set
            {
                base.ThemeClassName = value;
            }
        }
    }


We will try to address this in the upcoming service pack.

I hope this helps.