Here is a picture from The Inland Paper (volume 24) [that you can find here].
Since the paper was to be published in 1900, the editors were asked to provide their opinion on the writing of the number of that year in Roman numerals:
Here the difference is all a matter of economy, since both the notations are exceptionally allowed.
The Pupils' Arithmetic (...
As an Italian let me exercise my direct descendant rights by saying that "Bellum stellarium" sounds really ugly, "Bellum sidereum" has a much better feeling to it. And why not take the extra step and -thinking at the title of a movie- go for De bellis sidereis after Caesar's well know prequel.
I strongly disagree with C Monsour's interpretation of how the -ārius suffix works semantically. Stēllārius can perfectly mean 'of the stars', it is not tied to a singular interpretation ('of a star'). Sīdereus does have the advantage of being a classical word, used by many ancient authors even, much unlike stēllārius which isn't even medieval but modern, ...
@Joonas Ilmavirta treats "star" like an adjective. To me, "star" should be treated as a noun, in which case the translation becomes
(Disclaimer: I was raised to French & German translations of "Star Wars", where it is indeed translated as "war of the stars" -- bellum stellarum).
EDIT: based on the accepted answer, other candidates ...
Joonas' answer is right on grammar, but since we're not talking about a single star, an adjective based on sidus would have better semantics. I'd go with Bella Siderea.
Familiarity with modern Romance languages is not an unmixed blessing when translating into Latin. Often Latin has multiple words in the same semantic field with different shades of ...
Indeed, you cannot use a plain noun as an attribute in Latin the way you can in English.
Instead of "Star Wars" you have to say "Wars of Stars" or "Stellar Wars".
Adjectives are a very natural choice in Latin (whereas I would be tempted to choose genitives in Romance languages).
Bellum is indeed good for "war".
It is a matter of taste whether you choose ...