Able to reproduce this issue on reported version 66.0.3359.139 and latest canary 68.0.3430.0 using Mac 10.13.3, Windows 10 and Ubuntu 17.10. 

Good Build: 63.0.3238.0
Bad Build: 63.0.3239.0

NOTE: In Good build on selecting Norwegian-norsk , Norwegian is seen but from 63.0.3239.0 Norwegian Bokmål is seen.

You are probably looking for a change made after 508322 (known good), but no later than 508323 (first known bad).
CHANGELOG URL:
 https://chromium.googlesource.com/chromium/src/+log/e172457732b437d4e97b85bf763c91790e1897cc..497822f53905094e2d4b3c13fda5a834fb90505c

Reviewed-on: https://chromium-review.googlesource.com/683935

Suspecting same from changelog.

@ claudiomagni: Please confirm the bug and help in re-assigning if this is not related to your change.

Thanks!

Hi Yana, can you see if somebody in the Language team can look at this bug?

Let me know if you prefer if I look at it. Given my current load it might take me a long time before I can do it.

I suspect there's a mismatch between the language code in the "Add language" list and in the Preferences list.

Hey Claudio, we still only have one engineer on Language who just started full-time on it last week (Anthony) so if you could please take this on, we'd greatly appreciate it, especially given that this is a regression in the code you know best, and related to your change. 

@Yana: Okay, I'll work on it.
I've reduced priority to P2.

Can reproduce it as well on 70.0.3538.110.
What's the latest status on this issue, assuming that it's been created 6 months ago?

Thanks.