Runnable application for https://github.com/svenfuchs/i18n/issues/366

de.yml

de:
  customer: Kunde
  welcome: Willkommen, %{user}

i18n_bug.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'i18n', '0.8.1' # Broken
  # gem 'i18n', '0.8.0' # Works
end


class Customer
  def to_s
    I18n.translate(:customer)
  end
end

I18n.available_locales = %w(de de-DE)
I18n.locale = 'de-DE'
I18n.load_path = [File.join(__dir__, 'de.yml')]
I18n::Backend::Simple.include(I18n::Backend::Fallbacks)
I18n::Locale::Tag.implementation = I18n::Locale::Tag::Simple

puts I18n.translate(:welcome, user: Customer.new)