saas-one/frontend/operation-web/ext/classic/locale/overrides/pt_BR/window/MessageBox.js

Ext.define("Ext.locale.pt_BR.window.MessageBox", {
    override: "Ext.window.MessageBox",
    buttonText: {
        ok: "OK",
        cancel: "Cancelar",
        yes: "Sim",
        no: "Não"
    }    
});