To give the international and multilingual users a more cohesive chat experience, we’ve launchedBroadcaster Language Mode. Turn on Broadcaster Language Mode to let your community chat exclusively in your preferred language with other native language speakers.

Broadcasters When you select your Broadcast Language in your dashboard, you’ll have the option to opt-in to Broadcaster Language Mode. Once set, chat will be notified that Broadcaster Language Mode has been enabled, and chat will be restricted to users who speak your selected language. Broadcaster Language Mode is available on web and mobile, but can only be enabled on the Broadcaster Dashboard or in Broadcaster Options on your channel page.

Viewers When a channel has Broadcaster Language Mode enabled, you will be notified at the top of the chat. If your language settings match the broadcaster’s selection, you will be able to chat. Note: You can update your language settings at the bottom of the Twitch front page or in the left-hand column of any other page.

Multilingual? No problem! When Broadcaster Language Mode is enabled for a channel you’re on, you’ll be asked whether you speak the selected language. Just click the message to start chatting. We’ll save your preferences so you’ll be able to chat in any subsequent channel with Broadcaster Language Mode enabled for your languages.

Note: We use your preferred browser language to determine if you can chat by default in channels that have Broadcaster Language Mode enabled. However, any user can chat by indicating that you speak the broadcaster’s selected language. For example, if you prefer to use Twitch in English, but you’d like to chat in a channel that has Korean Language Mode turned on, just click the subsequent message asking if you speak Korean and you’ll be able to chat.
Even if Broadcaster Language Mode is enabled, all messages will be sent, regardless of language, so you won’t miss a single Kappa or PogChamp. Moderation is in the hands of the broadcaster and his/her moderators.

Moderators will always be able to chat, regardless of their preferred language.

WhispersYou will still be able to send and receive whispers in any language across any channel even if Broadcaster Language Mode is enabled.

via Twitch