Rails i18n Config Gotcha

20 Jan 2015

Today I battled a subtle problem which surfaced when our Rails application was updated from Rails 4.012 to 4.0.13.

Several tests started failing with I18n::InvalidLocale errors.

After some debugging I found that the following line of configuration config/application.rb was not being respected:

I18n.enforce_available_locales = false  

This line was introduced when the application was upgraded to Rails 4.0.2 a year ago. At the time, as this stackoverflow question highlights, the following deprecation warning message advised to do this:

[deprecated] I18n.enforce_available_locales will default to true in the future. If you really want to skip validation of your locale you can set I18n.enforce_available_locales = false to avoid this message.

However, as I digged deeper into the Rails 4.0.13 changes, I found that they included this commit, which changed the behaviour of setting i18n configuration values. It now ignores I18n.enforce_available_locales = false.

The solution is to follow the relevant section of the Rails Guides and configure as follows:

config.i18n.enforce_available_locales = false  

It’s a subtle change that caught us out.

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