richTextBox New file & Localization issue

Question

Hi all,
I'm new at C# and I created a simple text editor. I figured out have to load files in different formats such as txt and rtf and save content as well. Now I'm facing a new problem. searched around and didn't found solution. Under ToolStripMenuItem I have a link that supposed call for a new blank document. currently I user this.clear(); but it's not the way how it should be done. now I wonder how to call a new empty RichTextBox and when user have a unsaved entry how to check and alert user for saving entries.
 here is the code:

        private void ????????ToolStripMenuItem_Click_1(object sender, EventArgs e)

        {

            richTextBox1.Clear();

        }

then is there a way to use a separated language file for localization purpose  and how should I do or where should I look for solving these issues.
Thanks in advance.