Updated German help translation
Remove stale help translations

These translations have not been updated since the help rewrite over a year ago.
Updated Brazilian Portuguese translation for help
Add Files: disable the Add action if no file is selected

Based on a patch written by Srinivasa Ragavan

[bug #703187]
require glib 2.36

[bug #703552]
po/vi: import from Damned Lies
Updated Vietnamese translation
updated for version 3.9.4
Tajik translation updated
Updated Breton translation