I noticed today there's a newer viewer version (7.0.1). After downloading and extracting the portable version, I realized there are some files missing (especially *.lng files) from it when compared with 7.0.0.3. Is this a correct portable version or should we expect a newer one?
It's a correct version. In version 7.0.1 we started to integrate the lang files directly to the program to reduce clutter and increase certain aspects of security.
So if you try to change the interface language in the program you will see that all the languages are still there available.