One webmaster in John Mueller’s 09/24/2021 hangout was curious about a Spanish-version website they are working on.
The webmaster was concerned about showing users the wrong page based on their language, and they weren’t sure if they had the right technical implementation in place before they went live.
They could get a user there faster than using server-side redirects.
If you use a server-side redirect, then you risk showing only the redirected version to the user rather than the correct version.
With the banner approach, you have the opportunity to show the correct page to the right user more often.
This exchange takes place at the 21:25 point in the video: