you... say "hey you celebrate pascha too? Why don't we just do it together!" without ever knowing who these people are, what they believe in, etc.??
Not quite. The fundamental reason is that we don't tend to observe dates. Each church will probably hold its own services in its own building, though some will doubtless mount a joint service. I don't think anyone believes that Jesus was born on 25th December, or for that matter on 6th January. We just don't know, and as one of those dates has been used to celebrate his birth, they are as good as any. This is probably a contributing factor to our lack of interest in correctness of the date. Also, the whole idea of a church calendar has no place in our practice, apart from Christmas and Easter (and probably Whitsun).
With the Resurrection, I am aware that people believe they can calculate it correctly, though either Rome or Byzantium must be mistaken. But the actual date does not hold importance for us. The fact
does: so we are happy to accept the ambient dominant date.
What happens if you're in an area where there are SEVERAL celebrations of Pascha?
In Kosova where currently all the Evangelicals are Albanian and there is no Albanian Orthodox Church but there is a 4% Albanian Catholic minority and perhaps a 5% Serbian Orthodox minority, the Evangelicals follow the Catholic practice, but I suspect that is because it is Albanian rather than because they have given much thought to the actual date. In any case, the Albanian community is 96% Moslem, so the question of a dominant ambience does not come into play. In southern Albania, where there are some Catholics but 20% Orthodox, the Orthodox date is followed. It will be interesting to see what happens in the Republic of Macedonia (if I may use that name without offence) when an Evangelical church is established, for there are, as far as I know, no Albanian Catholic churches in the Albanian area and I have heard rumour of only one Albanian Orthodox church, in the deep south somewhere if it exists. There are probably fewer than a dozen Evangelical believers and no church, but if the community grows, it will be interesting to watch what they decide upon. You get the idea, but in regard to...
Ethiopia and Egypt, where you not only have ORthodox, Roman Catholics, but also COpts
I have no idea, but I guess
they follow the dominant practice, especially in places where the secular government awards a national holiday on the same date.
It seems like the date of the resurrection is not important, but rather just celebrating it,
in concert with other local christians
Less correct: it depends how ecumenically minded each congregation is. Some will have nothing to do with Catholics or compromised Liberal congregations. Personally, I would be quite happy, here in Wrexham, to join the open-air witness in which Catholics and Protestants join (we have no Orthodox church), because the only thing that event testifies to is the fact the Christ is risen from the dead. I can see no harm in joining with others to testify publicly to what we all agree on: but some would frown upon even that.
says, "There are very few Protestant churches with a liturgical calendar; in fact, most Protestants I know have no idea how Easter is calculated." He is right: I have no idea how the date is worked out, and I suspect that 99% of my fellows haven't any idea idea. If someone were interested in that question, I think it would be regarded as a rather odd but harmless pursuit, perhaps akin to my reading the homilies of Ælfric in the original.