English grammar rules about capitalization of book titles say that, basically, most every word is capitalized except middle articles, conjunctions and prepositions. So:
The author will see her book "A Star Shines the Brigthest when It's Falling" published next week.
In Spanish, rules are different, and only the first word must be capitalized (besides global rules like people's names and such). So if the above book were to have an Spanish edition, the Spanish news would go like this:
La autora verá su libro "Una estrella brilla más cuando es fugaz" publicado la semana que viene.
However, if Spanish news had to talk about the book using the English title (because e.g. a Spanish edition didn't exist), what rules are to be followed: English or Spanish ones?
? La autora verá su libro "A Star Shines the Brigthest when It's Falling" publicado la semana que viene.
? La autora verá su libro "A star shines the brigthest when it's falling" publicado la semana que viene.
As a bonus, though a bit offtopic, it'd be nice to know what is the norm in the opposite scenario: book titles in Spanish being used in English sentences.