While Zotero is primarily developed in English, most parts of the Zotero ecosystem have been translated into other languages. These include the Zotero client, the wiki documentation, and the Citation Style Language (CSL) citation styles.
Translation efforts for the Zotero client exist for over 40 languages, but many languages are still incomplete. To help localizing the Zotero client in your favorite language, sign up for free at https://www.transifex.com, go to the Transifex Zotero project page, and join a language translator team.
Note Translators should also check already translated strings, as some English strings have changed over time (predominantly to account for the move to Zotero as a standalone desktop app, rather than the Zotero for Firefox plugin).
Translations can be tested by changing the language of the Zotero interface.
The contents of the Zotero wiki can be translated into a number of languages. The top of each wiki page shows a row of language codes. You can move between languages by clicking a language code. Language codes are shown in black on a grey background if a page already exists for that language. Otherwise they are grey on a white background.
The languages currently available are (languages abbreviations follow ISO 639-1):
If you would like to translate the wiki into a language that is currently not available, feel free to post a request on the Zotero forums to have that language added.
For editing the Zotero wiki, see the information on writing Zotero documentation.
Zotero uses Citation Style Language (CSL) styles to format citations and bibliographies. CSL has advanced support for (automatic) localization of terms (e.g. “and” [English] and “und” [German]), date formats (e.g. mm/dd/yyyy [American English] and dd/mm/yyyy [Dutch]), and grammar rules.
CSL styles rely on a shared set of language-specific CSL locale files. Localization data can also be embedded in the styles themselves to override the data stored in these locale files.
To learn how to contribute to the collection of CSL locale files, and to see the status of translation, see the CSL locale repository wiki.