add i18n tests

spec/i18n_spec.rb

@@ -0,0 +1,12 @@
+require 'spec_helper'
+require 'i18n-spec'
+
+Dir.glob('config/locales/*.yml').each do |locale_file|
+  describe "#{locale_file}" do
+    it_behaves_like 'a valid locale file', locale_file
+    # We're currently allowing both German and English as source language
+    # besides, we're using localeapp, so that it's ok if pull requests
+    # don't have this - a localapp pull will fix that right away.
+    #it { expect(locale_file).to be_a_subset_of 'config/locales/en.yml' }
+  end
+end