Subject for とする


I need help figuring out who is the subject for とする in the below sentence

> 日本語を母語 **としない**
> 人の視点に立って、実際の使い方をわかりやすく解説します。([source](https://www.jpf.go.jp/j/project/japanese/teach/tsushin/grammar/))

I understand AはBとする as "A assume/regard B." But I can't apply this logic
to「日本語を母語としない人」. I can either understand it as

> **[somebody]** が日本語を母語としない人
>
> people who **[somebody]** don't assume they have Japanese as their mother
> tongue

or

> people who don't assume their mother tongue is Japanese

Which one is correct?




You say

> I understand AはBとする as "A assume/regard B."

You have the right idea but not quite the right implementation.

Let's use the word 'regard'. This word takes three components: X regards Y as
Z, where X is the subject, Y is the object and Z is the -- whatever you call
that in English. So the Japanese is Xは/がYをZとする. The thing that is getting
regarded is Y so this makes sense as the object, and using と makes perfect
sense here since it is a particle of comparison.

In your sentence the subject is 人, which is promoted to the head of the
relative clause so we have

> 日本語を母語としない人  
>  People (X) who don't regard Japanese (Y) as their mother tongue (Z)

**Edit** :

I deleted this answer because I thought that maybe using the word 'regard' was
a little misleading. I think XをYと思う would be more literal, but since you seem
confused about the assume/regard angle maybe I should try and say some more.

XをYとする literally means make X into/as Y. So I think "regard X as Y" is a
reasonable translation. When it comes to 'assume' I can think of two meanings
and I'm not sure which one you are thinking of. The first meaning would be 'to
make a judgment without evidence'. I don't think that fits here. The second
would be 'to take on a role/character/etc'. I guess 'people who take on
Japanese as a native language' kind of fits here but it's a bit awkward. I
think it is easiest just to think of the literal translation, 'make X as Y'
and mold it to the context using your native language.




AがBをCとする can mean “A has B as C”. So, 日本語を母語としない人 here means people whose
mother tongue is not Japanese.

