Very interesting question.
I really hope that we can somehow impact for the 2nd team's country or "nature of the country". Just those reasons mentioned earlier:
1) Language. The most important factor for me. If I do not understand anything in forums, I would definitely lose my interest to 2nd team. To be able to discuss, take part into forums, maybe contribute something would make me feel as part of the community.
2) Timing for league games. Schedule should be so that I'm not sleeping....preferred some evening times, not office hours. Chats in live followup are again big part of the game, at least in my local country.
Then third criteria is size of country, which is the most hard one to choose...
If purpose for this new possible feature is to get more active teams to micronations, I could live with that. I still wonder if this would impact for current "problems" related to micronations, would there be enough new active managers in every micronation so that competition would be much harder there, I doubt! Also putting money for 2nd team supporter in micronation....no. Joining micronation is just short experiment for me and for several others I'm afraid.
Today and now my choice would be a bigger and more competitive country: USA, even if timing is not necessarily optimal for me. Forums and competition seems to be my drivers now.