First include Ext.ux.Localizer.js

To localize a component just call Localizer.localize(component, locale): Localizer.localize(component, "nl");

The class looks for localized strings in "locales" property and if is not loaded tries to load it synchronously from ./app/locale/.js. Then for each component in the container looks for localizable properties and for each one looks for the equivalent translated value.

Ext.override(Ext.form.field.Checkbox, {
    setBoxLabel: function(boxLabel){
        var me = this;
    
        me.boxLabel = boxLabel;
        if (me.rendered) {
            me.boxLabelEl.update(boxLabel);
        }
    }
});