Right, I managed to make the Sitemap XML page work with the pr-BR language but this isn’t a ideal solution. I exclude the MO and PO files from pt-BR language (located in \wp-content\languages\plugins) and then updated the translation available for AIOSEO.
In the first access everything works as expected:
https://s31.postimg.org/z2qz7xl2j/image4.png
But from the second access the page back to the initial problem:
https://s32.postimg.org/ng7bqlmjp/image5.png