Monkey patch I18n.translate so it recognizes references encoded as ~> some.other.key

i18n_translate_with_references.rb

#
# config/initializers/i18n_translate_with_references.rb
#
module I18n
  class << self
    alias_method :original_translate, :translate

    def translate(*args)
      regexp = /\A~>(.*)\Z/ # e.g. ~> some.other.key

      if (original_translation = original_translate(*args))[regexp]
        referenced_key = original_translation.match(regexp)[1].strip
        translate(*args.slice(1..-1).unshift(referenced_key))
      else
        original_translation
      end
    end
  end
end

some_locale.yml

de:
  users:
    watch_lists:
      join:
        join_shared_watch_list: ~> users.watch_lists.index.join_shared_watch_list