How do I make a custom column text

I'm trying to follow the i18n id of this example, except my component will be a grid and I need to update the text of each column with a locale caption.

So I will have something like:

Code:

Ext.define('MyApp.view.MainPanel', {
    extend: 'Ext.grid.GridPanel',
    alias: 'widget.mainpanel',
    myField: 'MyColumnCaption',
    items: [
        {
            xtype: 'gridcolumn',
            dataIndex: 'myColumn',
            text: this.myField
        }
    ]
});

My problem is that I can only set a string for "text" in the architect (!) Meaning I can't use a variable as content. There is a type button on the left of the config panel in the architect, but it doesn't give me any other options than string.

Perhaps I'm expected to use data-binding, and apply the locale override on the databinding itself, but it's not what the sencha example is showing in any way.

How can I use a custom variable for the text property of a column ?

How do I make a custom column text