Fixed language error and added translation string.

There was a translation error in the German version that is fixed now.

There where still the English strings:
![language-error](https://cloud.githubusercontent.com/assets/2056876/5340065/72687a08-7ee8-11e4-9e93-cc6d3d646bd8.png)

Please change this to `tr("Failed to send file: %1").arg(fname)`. That way translators can reorder the words as necessary. :)