ChatGPT now supports a limited selection of languages in the interface:
Chinese (zh-Hans)Chinese (zh-TW)French (fr-FR)German (de-DE)Italian (it-IT)Japanese (ja-JP)Portuguese (pt-BR)Russian (ru-RU)Spanish (es-ES)
If you've configured your browser to use one of these supported languages, you'll see a banner in ChatGPT that enables you to switch your language settings. You can deactivate this option at any time through the settings menu.
This feature is in alpha, requires opting in, and currently can only be used on the web at chatgpt.com. Learn more here.