The walkthrough on the 12th had a tester on a Spanish phone sign in and watch the site turn English. The cause was simple: the account remembered the language it was made in, and sign-in applied it.
The first rule
The brief for the fix ranked the sources: a language in the address, then the device’s stored choice, then the account’s saved language, then the browser. The builder built it as written.
What the reviewer found
Two things. On a device with no stored choice, every page load showed the browser’s language for an instant and then the account’s, a visible flash. And the ranking itself left the original case broken: the tester’s Spanish phone had never picked a language, so it had no stored choice, and the account’s English still won.
The decision
The manager put the browser above the account, when the browser’s language is one the site has. The account’s language still decides emails, and it still decides the display for a browser in a third language. To kill the flash, the account’s language is remembered on the device under its own key for the first paint and cleared at sign-out. Changing the language in the song settings updates both the device and the account, so a second device with no choice of its own inherits it.
The manager made the call under the owner’s standing order to make progress without them, and recorded it as one the owner may reverse.