This currently is not possible with the standard widgets. However you could create your own button that requires context and set the label text to an attribute of the context object. That way you will have a dynamic label on your button that can change at any moment. However you will not be able to create a button on your controlbar.
You could try to setup a entity that contains the names and a key to retrieve the labels and then display these in an input box with some css styling to remove the box, so it will look like being a label. Not sure if this is what you're looking for though.
Ok. Let me rephrase my question. For eg. Based on some setting I need to change the label on a button from "Submit" to "OK". Is it possible to do this? I want to externalize the lable values.