PhoenixKit.Utils.RecipientLocale (phoenix_kit v2.16.0)

Resolves which locale a message should be rendered in for a given recipient.

Outbound messages (email, and the external notification channels) render on a background or request process that has no meaningful Gettext locale of its own — the sender's locale is not the recipient's. This module is the single answer to "whose language is this message in".

Where the preference lives

A user's dialect preference is stored full ("en-GB", "pt-BR") in custom_fields["preferred_locale"], written by PhoenixKit.Users.Auth.update_user_locale_preference/2 from the language switcher. Absent means the user never chose one.

Two consumers, two shapes

for_rendering/1 — for template lookup. Returns the full dialect and never nil, falling back to the site's content language and then "en". Template resolution does its own dialect→base narrowing ("en-GB" is tried before "en"), so handing it the dialect strictly beats pre-truncating.
base/1 — for Gettext, which keys on base codes and treats nil as "leave the current locale alone".

Installing it

in_locale/2 runs a function with a locale installed on the process, which is how a Gettext-backed default reaches the right language: these render on a background worker or on behalf of another user, so the locale arrives as a value rather than being ambient. nil means "leave the current locale alone" — what a screen rendering for its own viewer wants.

Failure

for_rendering/1 is total. The site default is read through PhoenixKit.Settings, which can raise on an unowned checkout or exit on a dead pool; both are caught and answered with "en". An unreachable database must degrade a message to English, never fail the send — this is the path PhoenixKit.Users.LoginAlerts calls during sign-in.

Summary

Functions

base(recipient)

The recipient's preference as a base language code, or nil.

for_rendering(recipient)

The locale to render a template in for recipient. Never nil.

in_locale(locale, fun)

Runs fun with locale installed on the process, restoring it afterwards.

preferred(arg1)

The recipient's stored dialect preference, or nil when they have none.

Functions

base(recipient)

@spec base(term()) :: String.t() | nil

The recipient's preference as a base language code, or nil.

For Gettext, which keys on base codes; nil means "no preference, leave the current locale alone".

iex> alias PhoenixKit.Utils.RecipientLocale
iex> RecipientLocale.base(%{custom_fields: %{"preferred_locale" => "pt-BR"}})
"pt"

for_rendering(recipient)

@spec for_rendering(term()) :: String.t()

The locale to render a template in for recipient. Never nil.

Preference → the site's content language → "en".

iex> alias PhoenixKit.Utils.RecipientLocale
iex> RecipientLocale.for_rendering(%{custom_fields: %{"preferred_locale" => "uk"}})
"uk"

in_locale(locale, fun)

@spec in_locale(String.t() | nil, (-> result)) :: result when result: term()

Runs fun with locale installed on the process, restoring it afterwards.

A nil locale runs fun untouched, so a caller with no recipient preference keeps whatever locale is already in force.

iex> alias PhoenixKit.Utils.RecipientLocale
iex> RecipientLocale.in_locale(nil, fn -> :ran end)
:ran

preferred(arg1)

@spec preferred(term()) :: String.t() | nil

The recipient's stored dialect preference, or nil when they have none.

Accepts anything: a %User{}, a plain map, or a bare email string (used by the magic-link registration path, where no account exists yet).

iex> alias PhoenixKit.Utils.RecipientLocale
iex> RecipientLocale.preferred(%{custom_fields: %{"preferred_locale" => "en-GB"}})
"en-GB"
iex> RecipientLocale.preferred("someone@example.com")
nil