Set it up once for the whole app

Every domain needs the AshGettext.Domain extension and a gettext block. Every resource needs the AshGettext.Resource extension. Instead of writing that in each one, write a base domain and a base resource once.

The base domain

defmodule MyApp.Domain do
  defmacro __using__(opts) do
    opts = Keyword.update(opts, :extensions, [AshGettext.Domain], &[AshGettext.Domain | &1])

    quote do
      use Ash.Domain, unquote(opts)

      gettext do
        backend(MyApp.Gettext)
        locale_resolver(MyApp.LocaleResolver)
      end
    end
  end
end

The base resource

defmodule MyApp.Resource do
  defmacro __using__(opts) do
    opts = Keyword.update(opts, :extensions, [AshGettext.Resource], &[AshGettext.Resource | &1])

    quote do
      use Ash.Resource, unquote(opts)
    end
  end
end

Use them

Write use MyApp.Domain where you wrote use Ash.Domain, and use MyApp.Resource where you wrote use Ash.Resource. Every other option works as before.

defmodule MyApp.Shop do
  use MyApp.Domain

  resources do
    resource(MyApp.Order)
  end
end

defmodule MyApp.Order do
  use MyApp.Resource,
    domain: MyApp.Shop,
    data_layer: AshPostgres.DataLayer,
    extensions: [AshJsonApi.Resource]
end

A resource or domain can still list its own extensions:. The base module adds AshGettext's extension to that list.

A domain that needs one setting changed writes its own gettext block with just that setting. The rest still comes from the base domain:

defmodule MyApp.Billing do
  use MyApp.Domain

  gettext do
    text_domain("billing")
  end
end

For an existing app

mix ash_gettext.install adds the extensions and the gettext block to every domain and resource you already have. Use it when you would rather not switch them to base modules.