How can I activate the pt_BR translation of Pro Sites

I tried using the Pro Sites localisation to pt_BR made by Marcelo Minholi (avaliable at https://premium.wpmudev.org/forums/topic/brazilian-portuguese-translation-for-pro-sites-plugin) but the translation won't load.
I have define('WPLANG', 'pt_BR'); set in my wp-config.
I copied the files to wp-content/plugins/pro-sites/pro-sites-files/languages. Both psts-pt_BR.po and psts-pt_BR.mo.
Other plugins in the same wordpress load the translations like a charm.
What am I missing here?