Updated Sept. 2024.
With LiveTL browser extension, you can translate YouTube live chat in real-time, making it easier to connect with creators and communities from around the world.
I've been using LiveTL for a bit now, and it's really easy to use. I am really impressed with how well LiveTL works, it translates almost instantly using Google Translate and it's been really helpful for me to be able to understand what's going on in the chat.
While LiveTL is also designed for Twitch, I haven't yet figured out how to make it work on that platform.
To get started with YouTube, after adding the extension to your browser, you need to enable the translation settings first. Open a YouTube live stream and look for the gear icon labeled "Hyperchat Settings" at the top of the live chat box.
Click the gear icon to open the settings, then scroll down to the bottom. You will see a checkbox for translation. Enable that option and select your desired target language. Once you've done this, the live chat will be translated in real-time.
There are times you may need to close and reopen the chat window for the translation to work.
Read also: YouTube Live Chat: Scrolling Across the Video