Seems to be affected by `$LANG` (or derivative) as for example this gives correct week number:
$ LANG=C ncal -w 01 2019
January 2019
Su 6 13 20 27
Mo 7 14 21 28
Tu 1 8 15 22 29
We 2 9 16 23 30
Th 3 10 17 24 31
Fr 4 11 18 25
Sa 5 12 19 26
1 2 3 4 5
$ echo $LANG
en_US.UTF-8
$ date +%V # this works correctly regardless.
18
pasi
