Except scripture stated that Japeth will dwell in the tabanacle of shem (i.d accept Christ). Europeans are considered as coming from Japeth so this makes more sense to why Europeans accepted Christ more than the children of shem and ham.
There can be two things correct at the same time. 1) Japeth peoples will convert, yes. 2). The lost 10 tribes will also reconvert.
What I dispute is the notion of Japeth nations being in Europe. St Isidore of Seville tied many historical nations as those who founded Europe. All of them have history going back to Israel.
Saxxons - Issac Sons - Sons of Isaac
The celts have all kinds of history tying them to King David.
The Scottish Declaration of Independence in the Middle Ages was sent to the pope and it tied the history of Scotland back to Jacob.
You should watch the video shared by Matthew a while back. Highly informative.