I dont think it's the whole picture but definitely a glimmer of it.
In the UK we have a huge immigrant population, I have a friend who is a qualified teacher and earns so little in his home country (Hungary) that he can work here on the minimum wage doing manual work and support himself and send money home too. It's mostly European such as Polish, Russian and Albanian.
We have publishers learning Albanian and I heard the other day one of them, (not even a pioneer) has 15 studies.
Imagine the picture painted though, you arrive in a strange country, are not altogether welcomed by it's people and suddenly you can join a group of happy, friendly people speaking your language.
Dont discount the baby boom though, remember the WT is far behind, when I had my children (14 years ago) it was much frowned on, now more and more couples are realising the end is nowhere close and are starting families late in life. This would account for publishers just coming up now.
Poppy