Fall back translations in unplugged pages

- Add helper for returning nil rather than error message on missing translations

Before (regression):

![image](https://cloud.githubusercontent.com/assets/206973/3630097/aab8c73e-0ea7-11e4-852f-e74aa0b6422d.png)

After (ignore font diff):

![image](https://cloud.githubusercontent.com/assets/206973/3630101/b2be27d0-0ea7-11e4-9eb0-c7344ea4be1f.png)