From the CIES: The notion of expatriates defines players having grown up outside the national association of their employer club and having moved abroad for sporting reasons. This definition allows us to isolate migrations directly linked to the practice of football. ... On the 1st of May 2018, 12,425 expatriate footballers were recorded in the 2,235 teams from the 142 leagues of 93 national associations surveyed. This figure includes first team squad members having been fielded in domestic league matches during the ongoing season. ... Expatriates represent 21.2% of players at global level (+1.2% compared to 2017). We came in #28, which they said amounted to 125 players, up one from the previous year's survey. Germany was the top destination. Mexico was #2 in CONCACAF. Brazil was #1 globally. Switzerland and Austria were one place above, and below, us, respectively. http://www.football-observatory.com/IMG/sites/mr/mr35/en/
The Japan Singapore pipeline is interesting. I can’t think of another team that plays in one league but has a team made of entirely players from a different country.