module I18n::Backend::Fallbacks

def extract_string_or_lambda_default!(options) 

def extract_string_or_lambda_default!(options)
  defaults = Array(options[:default])
  if index = find_first_string_or_lambda_default(defaults)
    options[:default] = defaults[0, index]
    defaults[index]
  end
end

def find_first_string_or_lambda_default(defaults) 

def find_first_string_or_lambda_default(defaults)
  defaults.each_with_index { |default, ix| return ix if String === default || Proc === default }
  nil
end

def translate(locale, key, options = {})

it is evaluated last after all the fallback locales have been tried.
only when it's a Symbol. When the default contains a String or a Proc
The default option takes precedence over fallback locales

usual.
locales it will then raise a MissingTranslationData exception as
the given options. If it does not find any result for any of the
(depends on the fallbacks implementation) until it finds a result with
locale :"de-DE" it might try the locales :"de-DE", :de and :en
locale given by I18n.fallbacks for the given locale. E.g. for the
Overwrites the Base backend translate method so that it will try each 
def translate(locale, key, options = {})
  return super if options[:fallback]
  default = extract_string_or_lambda_default!(options) if options[:default]
  options[:fallback] = true
  I18n.fallbacks[locale].each do |fallback|
    begin
      result = super(fallback, key, options)
      return result unless result.nil?
    rescue I18n::MissingTranslationData
    end
  end
  options.delete(:fallback)
  return super(locale, nil, options.merge(:default => default)) if default
  raise(I18n::MissingTranslationData.new(locale, key, options))
end