References:
Install spell checker
sudo pacman -S --needed hunspell
Install English dictionaries
sudo pacman -S --needed hunspell-en_us
Note: Install base-devel as described in aur.
Download Brazilian dictionary from AUR
git clone https://aur.archlinux.org/hunspell-pt-br.git
Make
cd hunspell-pt-br
makepkg -s
Install (replace <version>)
sudo pacman -U hunspell-pt-br-<version>-x86_64.pkg.tar.zst