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ex_cldr_trans is an ex_cldr-integrated fork of the excellent trans by @crbelaus. The enhancements in this library have been been submitted as a PR to trans. If the PR is accepted in the future then this library will revert to depending on it rather than maintaining a fork. Such a change will not affect the functionality or API in this library.

The documentation in cldr_trans is edited from the original trans documentation.



ex_cldr_trans provides a way to manage and query translations embedded into schemas and removes the necessity of maintaining extra tables only for translation storage. It is an addon library to ex_cldr.

ex_cldr_trans is published on and the documentation is also available online.


Optional Requirements

Having Ecto SQL and Postgrex in your application will allow you to use the Cldr.Trans.QueryBuilder component to generate database queries based on translated data. You can still use the Cldr.Trans.Translator component without those dependencies though.


Why CLDR Trans?

The traditional approach to content internationalization consists on using an additional table for each translatable schema. This table works only as a storage for the original schema translations. For example, we may have a posts and a posts_translations tables.

This approach has a few disadvantages:

  • It complicates the database schema because it creates extra tables that are coupled to the "main" ones.
  • It makes migrations and schemas more complicated, since we always have to keep the two tables in sync.
  • It requires constant JOINs in order to filter or fetch records along with their translations.

The approach used by Cldr.Trans is based on modern RDBMSs support for unstructured datatypes. Instead of storing the translations in a different table, each translatable schema has an extra column that contains all of its translations. This approach drastically reduces the number of required JOINs when filtering or fetching records.

Cldr.Trans is lightweight and modularized. The Cldr.Trans module provides metadata that is used by the Cldr.Trans.Translator and Cldr.Trans.QueryBuilder modules, which implement the main functionality of this library.



Imagine that we have an Article schema that we want to translate:

defmodule MyApp.Article do
  use Ecto.Schema

  schema "articles" do
    field :title, :string
    field :body, :string


Add a JSON column

The first step would be to add a new JSON column to the table so we can store the translations in it.

defmodule MyApp.Repo.Migrations.AddTranslationsToArticles do
  use Ecto.Migration

  def change do
    alter table(:articles) do
      add :translations, :map


Generate database function migration

ex_cldr_trans defines a Postgres database function to support in-db field translation. A migration task is provided to generate the migration required to define this function.

% MIX_ENV=test mix cldr.trans.gen.translate_function
* creating priv/repo/migrations
* creating priv/repo/migrations/20220307212312_trans_gen_translate_function.exs


Run migrations

Migrate the database to add the translations column and define the database function.

% mix ecto.migrate


Define a backend module

The next step is to define an ex_cldr backend module that defines the configured locales and other information for supporting localised applications. For example:

defmodule MyApp.Cldr do
  use Cldr,
    locales: ["en", "de", "ja", "en-AU", "th", "ar", "pl", "doi", "fr-CA", "nb", "no"],
    providers: [Cldr.Trans]


Note that for existing backend modules the only required step is to add Cldr.Trans to the list of :providers.


Add translations to schema

Once we have the new database column and the backend module, we can update the Article schema to include the translations:

defmodule MyApp.Article do
  use Ecto.Schema
  use MyApp.Cldr.Trans, translates: [:title, :body]

  schema "articles" do
    field :title, :string
    field :body, :string
    # use the 'translations' macro to set up a map-field with a set of nested 
    # structs to handle translation values for each configured locale and each 
    # translatable field
    translations :translations

  def changeset(article, params \\ %{}) do
    |> cast(params, [:title, :body])
    # use 'cast_embed' to handle values for the 'translations' map-field with 
    # a nested changeset
    |> cast_embed(:translations, with: &translations_changeset/2)
    |> validate_required([:title, :body])

  defp translations_changeset(translations, params) do

    |> cast(params, [])
    # use 'cast_embed' to handle values for translated fields for each of the
    # configured languages with a changeset defined by the 'translations' macro 
    # above
    |> cast_embed(:es)
    |> cast_embed(:fr)

After doing this we can leverage the Cldr.Trans.Translator and Cldr.Trans.QueryBuilder modules to fetch and query translations from the database.

The translation storage can be managed using normal Ecto.Changeset functions just like any other field. Leveraging changesets and the Phoenix.HTML.Form.inputs_for/2 helper, your HTML form for Article might look like:

<.form let={f} for={@changeset} phx-change="validate" phx-submit="save">
  <%= label f, :title %>
  <%= text_input f, :title %>
  <%= error_tag f, :title %>

  <!-- translations for 'title' field -->
  <%= inputs_for f, :translations, fn form_translations -> %>
  <%= for locale <- [:es, :fr] do %>
    <%= inputs_for form_translations, locale, fn form_locale -> %>
      <span><%= "#{locale}" %></span>
      <%= text_input form_locale, :title, placeholder: Map.get(, :title) %>
    <%= error_tag form_locale, :title %>
  <% end %>

  <%= label f, :body %>
  <%= text_input f, :body %>
  <%= error_tag f, :body %>

  <!-- translations for 'body' field -->
  <%= inputs_for f, :translations, fn form_translations -> %>
  <%= for locale <- [:es, :fr] do %>
    <%= inputs_for form_translations, locale, fn form_locale -> %>
      <span><%= "#{locale}" %></span>
      <%= text_input form_locale, :body, placeholder: Map.get(, :body) %>
    <%= error_tag form_locale, :body %>
  <% end %>

  <%= submit "Save" %>