Zotero's interface language defaults to matching the operating system's language. You can change the language to one of the options provided in the drop-down menu under Edit > Preferences > Advanced > General
To keep Zotero's user interface in one language, but to use another language for the citations and bibliographies created by Zotero, select the citation language you would like to use from either:
JURIS-M is an unofficial version of Zotero that allows you to store transliterations and translations of names, titles, and other fields, and create citations and bibliographies that show this information.
In the word processing program Zotero does create the footnote (or endnote), but it does so by passing a "create footnote" command on to your word processor. Any issues relating to the format of the footnote or what numbering style to use needs to be set in your word processor.