There is no requirement for the Night Qualification training to be given by an instructor with any specific qualifications or approval. This is because it is a Qualification, and not a Rating. So you can do it anywhere in the world, with any instructor at all.
I did mine in the US. There is one potential area of difficulty, and that is the requirement for solo flight. In the US, you can only fly an N-registered aircraft on an FAA license. If you have an FAA license that's based on your JAR license, it will have the same restrictions on it as your JAR license. Before you complete your training and sort out the paperwork, your JAR license (and therefore your FAA license) will be restricted such that you may not fly solo at night. But you can not complete the training without flying solo at night. The way around this is to get another FAA license - just a student license will do - which you can use to solo at night (although many people don't bother doing this, and the FAA don't really seem to mind).
I don't know the French or the Spanish regulations well enough to know if there would be similar complexities there, but certainly as far as the CAA are concerned there shouldn't be any problems.
FFF
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