If we choose the country of manufacture, most discs (especially R1) would be Mexican.
The original release of a DVD would not distinguish between language versions.
Surely the only sensible "locality" is the country that the DVD is marketed for, which usually is reflected in languages, subtitles and cover art.
And sometimes the choice will be difficult, since US-originated discs will usually only have one German language version for Germany, Austria and Switzerland combined (although a specific Swiss version might in addition have French text).

My logic was the reverse, without any Dutch text on the cover or the disc, it is unlikely to be a locality NL disc. Of course one has to look at what is actually on the disc to assess what its most likely destination is (since origin is covered in other places). In this particular case it may even be something generic for Europe.

The same DVD with exactly the same cover can be valid for more than one locality. This is specially true for music DVDs. I have seen music DVDs with more than one rating logo on the cover, so that it can be sold in several countries.