When switching the interface language on any topic while logged in as admin, a permanent error message appears: “Failed to preview theme because it doesn’t exist, or you don’t have permission to access it.” Regular users do not experience this issue. Steps to reproduce: Log in as admin Open any topic Switch the locale using the language selector Error message appears permanently — not briefly With regular user account — no error. Discourse version: 2026.1.3 [bug]

Issue resolved! It was caused by a stale ?preview_theme_id=6 parameter in the Chrome browser URL. Once removed, the error disappeared. Thank you for pointing that out!

No. Only Chrome. And this problem only appeared today. I just checked and other browsers don’t have this problem.

Do you see a ?preview_theme_id=ID in the browser’s address bar at any point? This error message is only shown if you’re previewing a theme with an incorrect ID. You likely did this at some point on this browser and that value “stuck” in the Chrome tab/window.

Error when switching locale: "topic doesn't exist" message appears on all topics

Product Support

pmusaraj (Penar Musaraj) April 16, 2026, 2:11pm 2

Do you get this issue on a different browser with the same admin user?

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Error when switching locale: "topic doesn't exist" message appears on all topics

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