The following code requires you to setup a new custom message in Applications (Application Developer Responsibility) with name XXX_CUSTOM_MSG_BUTTON.
OASubmitButtonBean oasb =
(OASubmitButtonBean)pageContext.getWebBeanFactory().createWebBean(pageContext,
"BUTTON_SUBMIT");
oasb.setID("xxCustomButton");
oasb.setUINodeName("xxCustomButton");
oasb.setEvent("xxCustomButton");
String printTextMsg = pageContext.getMessage("XXX","XXX_CUSTOM_MSG_BUTTON",null);
oasb.setText(printTextMsg);
oawebbean.addIndexedChild(oasb);