PO metadata shown as translation for empty language tags

[osma]

At which URL did you encounter the problem?

http://finto.fi/cn/fi/page/2513A

What steps will reproduce the problem?

1. Go to a concept which has a label without language tag (e.g. above URL)
2. Look at the labels

What is the expected output? What do you see instead?

Seeing a bunch of PO file metadata. This happens because the empty language tag is translated via gettext, and the empty msgid is special in PO files.