[question] How to set the Devise locale for current request (in a thread safe manner)?

[collimarco]

Currently I use this code as suggested by the Rails guide:

  # application_controller.rb

  around_action :switch_locale
  def switch_locale(&action)
    locale = params[:locale] || I18n.default_locale
    I18n.with_locale(locale, &action)
  end

This is thread safe and works perfectly for the application... but not for Devise! Devise keeps using the default language (even if the translated YML files are present).

What should I do in order to tell Devise the language for the current user?

I know that there is I18n.locale but it is not thread safe...

[collimarco]

It seems that some flash messages from devise are translated and others are not.

It may be related to this:
#145

In order to reproduce the issue:

1. try login with an invalid password
2. you get an error message (flash) in the wrong language (the default, not the current)

If you log in successfully, instead, the flash message is in the correct language.

[JasonBarnabe]

I doubt the issue is in this project. Can you take a look at heartcombo/devise#4823 to see if anything helps in there?

[JasonBarnabe]

I did some testing...

• If you set locale in before_action with I18n.locale =, then both your app and Devise's error messages are translated properly.
• If you set locale in around_action with I18n.with_locale, then your app's messages are translated properly, but Devise's error messages are not.

Presumably in the around_action case, the error message is being generated outside the I18n.with_locale block. I'm not sure if this would be considered a bug, but I found wardencommunity/warden#180 that seems to reference the issue.

[excid3]

I got looking into this today.

Setting I18n.locale= is thread safe.

https://github.com/ruby-i18n/i18n/blob/3269c01edf3bb9537602bf0467a6bab38b3d9ba6/lib/i18n.rb#L41-L62

From this thread where they discussed changing it in the Rails guide. The change was not made for thread safety as Xavier points out. That's lead to some confusion, but it's safe to use a before_action with I18n.locale=

[JasonBarnabe]

I've updated the readme to warn against using around_action and I18n.with_locale as described in the Rails guide. There isn't anything to fix in this project - the issue looks like it's in wardencommunity/warden#180.