Some CSL citation styles, such as the Chicago Manual of Style styles, convert titles to title case. However, title casing is specific to English. To prevent non-English titles from being title cased, specify the language of the corresponding item in your Zotero library using the “language” field.

Use two-letter language codes, e.g. “de” for German, “fr” for French, or “ja” for Japanese (four-letter codes can also be used, e.g. “de-DE” and “ja-JP”; see https://github.com/citation-style-language/locales/wiki for a list of locale codes). English items can be marked as such using “en”, “en-GB” (British English) or “en-US” (American English).

Titles should generally always be stored in sentence case; Zotero can automatically transform titles into title case, but items cannot be reliably transformed to sentence case (e.g., while treating abbreviations and proper nouns correctly). See Sentence Casing for more information.