Set the language in the item record
Citations in bibliographies and footnotes are only as good as the accuracy of information in the fields of the Zotero item. If you're working in multiple languages and your citations are incorrectly capitalized, try telling Zotero what language the item is in so that the citation style can apply punctuation and capitalization rules appropriately.
Multilingual Zotero (MLZ)
MLZ, or Multilingual Zotero, is sometimes the answer for those researchers who work with non-Roman alphabets.
However, you can't have both Multilingual Zotero and regular Zotero installed. You'd need to choose. (But it is possible to transfer libraries if you change your mind.)
More information and download link: CitationSytlist