Capitalization of English book titles in Spanish text

Question

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.

Answer 1

In Spanish, Fundéu recommends using Spanish rules for capitalization, though using those in the original language is also admissible.

Spanish Wikipedia uses the original title in its articles for foreign works (if only because the translation can be different in different Spanish speaking countries), and the criterion there is respecting the original capitalization. For instance: One Flew Over the Cuckoo's Nest.

As for the offtopic bonus, the general use in English is to respect the original as much as possible always, sometimes even using non-English characters. English Wikipedia uses original capitalization, as we can see in the article on Mujeres al borde de un ataque de nervios; the different capitalization can be seen at the beginning of the article.

In summary:

• In Spanish, using Spanish capitalization rules (RAE see 4.17) is recommended, though using the original is admissible
• In English, use the original capitalization