The pt-br version of the app only allows to edit the pt wikidata description of the articles instead the pt-br, pt-br is a available language on wikidata too.
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This will not be feasible, since pt-br is not an official variant on Wikipedia, just like en-gb is not an official variant of English.
https://meta.wikimedia.org/wiki/Requests_for_new_languages/Wikipedia_Brazilian_Portuguese