Typically, English titles are capitalised according to the "title style" or the "headline style", which means that the main words are capitalised: Zotero: A Guide for Librarians, Researchers, and Educators. In French, German, Spanish or other languages, the capitalization rules are different. Most styles adapt the capitalisation to the language of the reference, if you fill in the "language" field of the reference: fre, ger, spa...