Anything covered in Subpart B does not apply outside of the US, for example 91.171 VOR check. You must comply with the state regulations in which you are operating.
Subpart B—Flight Rules
General
Sec. 91.101
Applicability.
This subpart prescribes flight rules governing the operation of aircraft within the United States and within 12 nautical miles from the coast of the United States.
Hmmm… that is really interesting!
Especially as one pilot reported, a few years ago, getting ramp checked in France and the policeman having a briefing pack listing VOR checks 
NCYankee wrote:
Anything covered in Subpart B does not apply outside of the US, for example 91.171 VOR check.
I’ll be darned. Especially because 91.171 actually mentions means of compliance “outside the United States” multiples times.
Here is an example of the wording for a different Subpart:
Subpart E—Maintenance, Preventive Maintenance, and Alterations
Sec. 91.401 Applicability.
(a) This subpart prescribes rules governing the maintenance, preventive maintenance, and alterations of U.S.-registered civil aircraft operating within or outside of the United States.
I suspect that the wording in 91.171 is allowing for the check to be performed outside of the US, but it is only applicable inside the US as requirement for using the VOR because of the wording in 91.101. I don’t think the US can dictate flight rules for other states, but they may accept tests performed by appropriate authorities in other states.
I would simply check the set VOR radial against the magnetic bearing of the GPS to the VOR.
That would work on some GPS systems, but not on others, especially in the US where the VOR’s are not realigned frequently, if at all. Some GPS will show a bearing based on current variation while others will base it on the declination (original or most current variation from a realignment) of the VOR. The difference can be 6 degrees in some cases. Radials are based on the variation of the VOR alignment, not current variation.
I am trying to work out what the problem is in this case.
AFAIK European VORs get adjusted regularly; most likely over a secure data link (they have a telephone line).
So… if I have this right, you are flying towards e.g. SFD
with GPS, DCT SFD, on a GPS (magnetic) track of 090.
The NAV receiver (EHSI or whatever) with 090 set on the OBS should indicate with a bar centred and a TO flag.
That is how I have always been doing VOR tests and both receivers have been within 1 degree.
The interesting Q is where would this not work.
If the VOR has not been adjusted and is say 5 degrees off then you need to be able to look up that error and allow for it, but is this ever the case in Europe?
It is a tremendous amount of work to adjust a VOR to an updated variation. Every route, intersection, approach, SID or STAR based on the VOR needs to be adjusted and flight tested. Coordinating this with the actual change and all affected charts is another big hassle.
As a comparison, in California, OAK was last aligned in 1975, 42 years ago, and at the time the variation was 17 degrees East. The current sectional shows the magnetic variation to be 13.75 degrees East. There is an airway between OAK and waypoint SALAD on the 060 degree radial, but the GPS uses the current magnetic variation and shows the track to be 064 degrees.
Using ForeFlight to scan the VOR orientation, I notice a distinct difference in Europe and the US, all the VOR’s in Europe seem to be aligned to true north whereas in the US, it is obvious they are aligned to magnetic north. So maybe Europe took the strategy of aligning radials to true north and not magnetic north. The obvious advantage is the radials would be unaffected with changes in variation, but they would differ from what a GPS would be using, as it uses magnetic variation. By publishing a changing declination periodically for each VOR, a GPS could use that information to describe the correct radial when going direct to a VOR.
Here is an interesting site that one can use to lookup historical declination https://maps.ngdc.noaa.gov/viewers/historical_declination/
NCYankee wrote:
…all the VOR’s in Europe seem to be aligned to true north…
No, VORs are aligned with magnetic north in Europe too. But the magnetic variation is generally very low in Europe (less than 5 degrees almost everywhere).
