Heroku does not seem to be loading config/locales/pt.yml. (Language is being set correctly to pt.)
I18n is working perfectly on localhost,
I ran into a similar issue, but mine was due to having duplicate keys.
In one file, we defined this:
en:
dashboard: "Dashboard"
And another we defined
en:
dashboard:
title: "Some Title"
Locally, I18n.t("dashboard.title") worked just fine, but on production it did not. The reason was probably due to a load order difference between Heroku and my development machine.
I fixed it by changing the name of the first dashboard key so there was no longer an overlap.