That's because most of it isn't true.
Elaborate, please.
As semimojo indicated these statments about Japan are false.
All in all it is true that Japan has overall strict immigration policies preventing uncontrolled third-world mass immigration and a strong local cultural identity that disfavors the creation of hostile parallel cultures.
However it is not true that Japan specifically bans muslim immigration or prohibits intermarriage. That’s utter nonsense.
As one particular example: since the 1980’s there are ten thousands of Iranians who came as guestworkers in Japan - many have stayed. Now it is businessmen and also students from various majority islamic countries that have a presence in Japan.
There also are mosques in Japan:
https://en.wikipedia.org/wiki/List_of_mosques_in_Japan
Regarding Arabic/Islamic studies:
Arabic Studies in Tokyo University of Foreign Studies:
http://www.tufs.ac.jp/english/education/ug/studies/arabic.html
There even is a Saudi-funded “Arabic Islamic Institute” in Tokyo: http://www.aii-t.org/e/
Islamic School in Osaka:
http://iiso-jp.org/