Return translation string if fallback locale is not available

Author: Morred

lib/grape/exceptions/base.rb

@@ -74,7 +74,12 @@ def translate(key, **options)
         options = options.dup
         options[:default] &&= options[:default].to_s
         message = ::I18n.translate(key, **options)
-        message.present? ? message : ::I18n.translate(key, locale: FALLBACK_LOCALE, **options)
+        message.present? ? message : fallback_message(key, **options)
+      end
+
+      def fallback_message(key, **options)
+        return key unless ::I18n.available_locales.include?(FALLBACK_LOCALE)
+        ::I18n.translate(key, locale: FALLBACK_LOCALE, **options)
       end
     end
   end

spec/grape/exceptions/base_spec.rb

@@ -9,21 +9,30 @@
 
     context 'when I18n enforces available locales' do
       before { I18n.enforce_available_locales = true }
-      after { I18n.enforce_available_locales = false }
+      after do
+        I18n.available_locales = %i[de en]
+        I18n.enforce_available_locales = false
+      end
 
       context 'when the fallback locale is available' do
-        before { I18n.available_locales = %i[de en] }
+        before do
+          I18n.available_locales = %i[de en]
+          I18n.default_locale = :de
+        end
 
         it 'returns the translated message' do
           expect(subject).to eq('cannot convert String to xml')
         end
       end
 
       context 'when the fallback locale is not available' do
-        before { I18n.available_locales = %i[de jp] }
+        before do
+          I18n.available_locales = %i[de jp]
+          I18n.default_locale = :de
+        end
 
-        it 'currently raises an error' do
-          expect { subject }.to raise_error(I18n::InvalidLocale)
+        it 'returns the translation string' do
+          expect(subject).to eq("grape.errors.messages.#{key}")
         end
       end
     end