Mercurial translations are not accessible

I want to use the pt_BR translation of Mercurial help. I've changed LANG, LC_ALL and even LANGUAGE to pt_BR but Mercurial is still using the english text.

The Mercurial's pt_BR translation is present at /usr/share/locale/pt_BR/LC_MESSAGES/hg.mo however, Mercurial seeks for it at another path: /usr/share/locale-langpack/pt_BR/LC_MESSAGES/hg.mo

Steps to reproduce:

export LANG='pt_BR'
strace -o trace.log hg version
grep pt_BR trace.log

Result:

stat("/usr/share/mercurial/locale/pt_BR.ISO8859-1/LC_MESSAGES/hg.mo", 0x7fff2da0e4d0) = -1 ENOENT (No such file or directory)
stat("/usr/share/locale-langpack/pt_BR.ISO8859-1/LC_MESSAGES/hg.mo", 0x7fff2da0e4d0) = -1 ENOENT (No such file or directory)
stat("/usr/share/mercurial/locale/pt_BR/LC_MESSAGES/hg.mo", 0x7fff2da0e4d0) = -1 ENOENT (No such file or directory)
stat("/usr/share/locale-langpack/pt_BR/LC_MESSAGES/hg.mo", 0x7fff2da0e4d0) = -1 ENOENT (No such file or directory)

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: mercurial 4.5.3-1ubuntu2
ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
Uname: Linux 4.15.0-20-generic x86_64
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun May 20 11:39:54 2018
InstallationDate: Installed on 2018-05-13 (7 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
SourcePackage: mercurial
UpgradeStatus: No upgrade log present (probably fresh install)