Google announced that it has made it easier to translate YouTube video captions into over 300 languages.
"You’ll first need a caption track for your video, so if you don’t yet have one you can learn how to make one here," the company explains in a blog post. "Select 'Request translation' in the YouTube Video Manager, choose the languages you’d like to translate into, and click “Next.” We’ll create caption translation documents that you can now invite anyone to help translate, or you can translate yourself. To translate the captions yourself, select the language, and it’ll open up the caption translation document in the Google Translator Toolkit editor to help your translate faster."
"To give you context on the captions, we’ve also embedded the YouTube video in the editor so you can watch as you translate," the company notes. "For several languages we’ll provide first draft of the translation using Google’s machine translation technology. We’ll also provide preview of what the translated caption looks like on the video so you can make sure the translated captions fit."
After all of that, just click "Publish to YouTube".
If you need more instruction, YouTube has a help center article on the topic.