Hunspell cannot find dictionary

Can't open affix or dictionary files for dictionary named "en_GB". arch linux

I first thought this was an Emacs problem, but it turned out to be hunspell itself. Running it from the command line showed:

$ hunspell -D
SEARCH PATH:
.::/usr/share/hunspell:/usr/share/myspell:/usr/share/myspell/dicts:/Library/Spelling:/home/torstein/.openoffice.org/3/user/wordbook:/home/torstein/.openoffice.org2/user/wordbook:/home/torstein/.openoffice.org2.0/user/wordbook:/home/torstein/Library/Spelling:/opt/openoffice.org/basis3.0/share/dict/ooo:/usr/lib/openoffice.org/basis3.0/share/dict/ooo:/opt/openoffice.org2.4/share/dict/ooo:/usr/lib/openoffice.org2.4/share/dict/ooo:/opt/openoffice.org2.3/share/dict/ooo:/usr/lib/openoffice.org2.3/share/dict/ooo:/opt/openoffice.org2.2/share/dict/ooo:/usr/lib/openoffice.org2.2/share/dict/ooo:/opt/openoffice.org2.1/share/dict/ooo:/usr/lib/openoffice.org2.1/share/dict/ooo:/opt/openoffice.org2.0/share/dict/ooo:/usr/lib/openoffice.org2.0/share/dict/ooo
AVAILABLE DICTIONARIES (path is not mandatory for -d option):
Can't open affix or dictionary files for dictionary named "en_GB".

So, I tried the most obvious thing, search for a hunspell dictionary for English. I thought English was installed by default, but alas:

$ pacman -Ss hunspell english
extra/hunspell-en_au 2020.12.07-5
    AU English hunspell dictionaries
extra/hunspell-en_ca 2020.12.07-5
    CA English hunspell dictionaries
extra/hunspell-en_gb 2020.12.07-5
    GB English hunspell dictionaries
extra/hunspell-en_us 2020.12.07-5
    US English hunspell dictionaries

None of these were installed by default. To get the British dictionary, I just did:

# pacman -S extra/hunspell-en_gb