One thing that's annoying about diy.SE is that so many people are asking location-specific questions (eg electrical questions about the NEC, which are specific to the USA; things are completely different in Europe) and there is no way to a) identify the location the poster is asking about (mostly lots of assumption about the USA), or b) filter on locales of interest. A rule that questions must have a country tag and optionally a region tag (eg USA/Maine, Canada/Ontario, France, UK/Scotland, Germany/Bayern) would help readers understand the context.

I'm all for adding location tags where it's relevant. For example, asking about wiring requirements for the US as you point out.

Something that I find annoying about diy.SE though (in fact, more so than missing location), is when location is obvious and/or doesn't matter, some people come in and badger the asker about the location tag just as a way to participate in the conversation despite having nothing to contribute. For that reason I would be against making it compulsory. It should be up to the asker to decide whether it's worth making the question more specific and getting more detailed answers. If answerers don't like it, they can always simply not answer.

The problem with optional location tags is that you can't filter when there are no tags. Construction is so different between countries and that's not just electrics (eg USA stick framing, UK brick/block cavity wall, Mediterranean reinforced concrete frame). So many people on diy.SE assume that it's a USA site with a USA audience, and so no USA tag is needed, which means that a big chunk of questions have a built-in USA assumption. If questions have no location tags, you can't filter questions that are relevant to your situation/experience.

That said, another option would be to insist people add a non-zero number of tags, and just say 'please specify your location in a tag' rather than insisting on a location tag per se. 'How do I repair my hammer' probably doesn't need a location, for example.

Well the second paragraph sounds good to me - by the way, I think you are already required to add at least one tag. Although often people fill that requirement with a topic tag, not a location tag. I guess it seems strange to ask a question tagged only with a location.

There is also a common situation where people ask a question where location is important, but are not aware of that it is. A comment saying to add a location tag seems like a good way to deal with those.