You could propose they clarify the instructions. You are not the first on (neither was I) who tripped over this

Merge .pot into all locales
mix gettext.merge priv/gettext

It never mentions when or where ‘all locales’ are defined.

Did you run mix gettext.merge priv/gettext --locale {locale} to create a locales’ folder? This creates a priv/gettext/{locale} folder with the files.

Once you have done so for each locale you want to support, you can use mix gettext.extract --merge.

If you’re on elixir 1.15 then I think you’re running into this issue: Running `mix gettext.extract` doesn't extract new messages with Elixir 1.15 · Issue #367 · elixir-gettext/gettext · GitHub

It’s fixed on the main branch, but not yet released. You can temporarily depend on the github version in your mix.exs, it my hypothesis is correct.

You don’t need to configure :priv (and :default_locale?) if they are default like that. You probably triggered a full recompilation somehow.

If you’re not on Elixir 1.15 then all the above doesn’t hold.