We need to review unused strings in the VPE:
1. Delete messages which are already obsolete.
2. Change concatenating externalised strings like:
InvalidFilename1=The filename '
InvalidFilename2=' is not valid
to something like:
InvalidFilename=The filename ''

'' is not valid.
3. Add NON-TRANSLATABLE comments where they are needed.

Also see JBIDE-4044.