Which languages are not used as systems default even by their native speakers?

Hello,

in addition to this initial question by me

     https://lists.debian.org/debian-i18n/2023/09/msg00016.html

I would like to ask you for languages that are not used as systems 
default by their nativ-speakers.
This question is related to package "backintime" [1][2] and will result 
in a new feature.

One example might be Faroese. Some of them do use English or Danish as 
systems default. There are several reasons why this happens. But this is 
IMHO not relevant for this thread here.

Another that comes into my mind is Traditional Chinese. I assume most of 
its users do use Simplified Chinese.

The idea is to "identify" such users (e.g. who setup "Danish") and 
remind them at the first(!) start of an application that this 
application do offer its GUI in a language (e.g. Faroese) that might fit 
better to their needs or native language.

To implement something like this I need such a list of languages:
    Danish -> Faroese
    Simpl. Chinese -> Trad. Chinese
    Norwegian Bokmål -> Norwegian Nynorsk
    Norwegian Nynorsk -> Norwegian Bokmål
    etc

This won't catch everyone or every language. For example lot of users 
speaking such "minor" languages just use English as default language. I 
can't catch them. Or I have to give them a list of 44 languages [3] they 
might check just because they do use English.
For example Esperanto is another example. Esperanto speaking users are 
using different system default languages.

But there might be other "clear" examples like Faroese?
Do you have more examples?

[1] -- <https://tracker.debian.org/pkg/backintime>
[2] -- <https://github.com/bit-team/backintime>
[3] -- <https://translate.codeberg.org/projects/backintime/common/>