@macrocallback compile_interpolate(translation_type(), message :: String.t(), bindings()) ::
  Macro.t()

Called to perform interpolation at compile time.

@callback message_format() :: String.t()

Defines the Gettext message format to be used when extracting.

The default interpolation module that ships with Gettext uses "elixir-format".

See the GNU Gettext documentation.

@callback runtime_interpolate(message :: String.t(), bindings()) ::
  {:ok, String.t()}
  | {:missing_bindings, partially_interpolated_message :: String.t(),
     missing_bindings :: [atom()]}

Called to perform interpolation at runtime.

If successful, should return {:ok, interpolated_string}. If there are missing bindings, should return {:missing_bindings, partially_interpolated, missing} where partially_interpolated is a string with the available bindings interpolated.