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

Ext.define("Ext.locale.es.window.MessageBox", {
    override: "Ext.window.MessageBox",
    buttonText: {
        ok: "Aceptar",
        cancel: "Cancelar",
        yes: "Sí",
        no: "No"
    }    
});