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Google's John Mueller said that Google Search tries "to find the primary language per page." So when you mix languages, that might cause issues with Google doing that. He added on Twitter "but what you put on different pages is totally up to you."
Here is that tweet:
Sure, no problem. We try to find the primary language per page, but what you put on different pages is totally up to you.
— 🍌 John 🍌 (@JohnMu) July 11, 2021
Now, John said this numerous times before. In 2010, yes, over ten years ago, John Mueller talked about Google's one language per page rule. In 2014 he described examples of where mixing languages can cause issues in Google Search. In 2018, John said try not to mix languages in your title tags.
Sure. I'd just avoid the situation where you have multiple language versions of the same text on a page (eg translation next to the original). Make it easy to recognize the primary language.
— 🍌 John 🍌 (@JohnMu) July 14, 2021
I am sure I've covered this other times but it seems like it is best to try to stick to one language per page, not just for SEO purposes but also probably for your website visitors.
Forum discussion at Twitter.
