While I don't find it necessary to localize NB as
a whole, there are some things which every now and
then raise issues which depend on the user's language.

The two prominent examples are keyboard shortcuts
(see Issue 39502 or Issue 41477)
and abbreviations (see Issue 16310)

It would be very useful to have some kind of
localized 'profiles' for things like these. That
way there could be an additional (german, danish,
...) profile which overrides shortcuts which don't
work on the corresponding keyboard layout or
abbreviations which conflict with common words of
that language.
These profiles could then easily provided with NB
installers or modified and shared by users.
I imagine it wouldn't be too hard to find
volunteers to manage those profiles for their own
language.