How to improve translations lang-ja

[dimaqq]

Got a comment from a native speaker:

I think this notation is confusing.
(In Japan?) some people think the week starts on Monday and others think it starts on Sunday (I guess Monday starts may be the mainstream...)
So - some people think that 翌週の日曜日 is next week, while others think it is 2 days later [today is Friday].

[dimaqq]

May be of interest to @ta-kiyama
Source code is at https://github.com/date-fns/date-fns/blob/master/src/locale/ja/_lib/formatRelative/index.js