"Acest străin este de naționalitate română."

Translation: This stranger is of Romanian nationality.

[AriW1977]

Cuvântul "străin" se poate traduce și drept "foreigner" în engleză

[Lacusta]

'foreigner' is indeed the correct translation in this context.

[JustSeiyin]

why is "de" being used for "of" instead of the genetive case of nationality?

[Miepsa1]

I think it is more correctly to say, that this stranger has the romanian nationality....

[8OhQ2fAw]

Could we use "românească" în loc de "română"? Is there a difference?

[8OhQ2fAw]

Ok, here is the answer I've found and might be useful for other people:

"It doesn't help that in English we use the same word when in Romanian there are 3 words used with 4 separate uses: a noun 'român', an adjective 'român' to describe a person and the language, an adjective 'românesc' to describe objects, and an adverb 'româneşte' to describe the way someone is speaking or writing."

[Miepsa1]

în loc de; instead of; in plaats van.....

[ANfg91]

This sentence could make sense if used to explain that someone, who people were thinking was a stranger (but were not wanting to label a foreigner) was actually a Romanian passport holder.
So in future will often apply to people born and brought up elsewhere but from Romanian families!