Comment 1 for bug 282017

I have never tried entering Japanese but it is almost sure that the
regular Mac OS X way won't work: Inkscape is not a "true" OS X
application since it runs in X11. In particular it does not use the
text system of Mac OS X. Therefore, you need to figure out how to
enter japanese under X11/GTK, how you would do in Linux for example.
For that I am sorry but I cannot help. Many other people can. I know
you can write arabic in Inkscape in Mac OS X, so there must be a way
to input Japanese.
Sorry that it may disappoint you. I hope that you will find a solution