Edit in JSFiddle

tinymce.init({
  selector: 'textarea',
  plugins: 'code,Button1, Button2, Button3 ',
  toolbar: 'alignleft,aligncenter,alignright | code | Button1 | Button2 | Button3',
  statusbar: false,
  menubar: false
});

tinymce.PluginManager.add('Button1', function(editor, url) {
  // Add a button that opens a window
  editor.addButton('Button1', {
    text: 'ボタン1 ',
    icon: false,
    onclick: function() {
      editor.insertContent('{!!ボタン1!!}');
    }
  });
});
tinymce.PluginManager.add('Button2', function(editor, url) {
  // Add a button that opens a windo
  editor.addButton('Button2', {
    text: 'ボタン2 ',
    icon: false,
    onclick: function() {
      editor.insertContent('{{ボタン2}}');
    }
  });
});
tinymce.PluginManager.add('Button3', function(editor, url) {
  // Add a button that opens a window
  editor.addButton('Button3', {
    text: 'ボタン3 ',
    icon: false,
    onclick: function() {
      editor.insertContent('[ボタン3]');
    }
  });
});
<textarea></textarea>
body {
  padding: 5px;
}