#4 Indicate empty translations on per language basis

[Misha Gavryuchkov]

Since it is not one person who does the translations -
most probably there are as many of them as languages,
then the exclamation mark shows only the fact that SOME
LANGUAGE or languages are empty but does not give a
sense who (which translator) has to go to this key and
do the translation.
Possible solution is to add a popup tooltip to the key
to indicate which language is missing.