@spec translate(list() | struct() | map(), list() | String.t() | atom(), keyword()) ::
  list() | struct() | String.t()

Translates an Ecto struct, a list of Ecto structs or a map containing translations.

Translating an Ecto struct for a given locale consists of the following steps:

1. Get the list of the fields that need to be translated from the Schema. The Schema must contain a get_translatable_fields\0 function returning a list of those fields.

2. Get the text for the given locale and store it into a virtual field. The Schema must provide, for each translatable field, a corresponding virtual field in order to store the translation.

3. Get the list of the associations that also need to be translated from the Schema. The Schema must contain a get_translatable_assocs\0 function returning a list of those associations.

4. Repeat step 1. for each associated Ecto struct.

@spec translate!(list() | struct() | map(), list() | String.t() | atom(), keyword()) ::
  list() | struct() | String.t()

Same as translate/3 but raises an error if a translation is missing.