The focus-management section is especially important. Replacing part of a page visually does not guarantee that keyboard or screen-reader users know where the new content appeared. Moving focus to a result heading makes the enhanced flow much clearer.
Starting with a working HTML form is a strong architectural constraint. It ensures that the primary task survives slow scripts, deployment mismatches, and runtime errors, while JavaScript remains responsible for improving the transition rather than rescuing the entire experience.
Checking for both missing and obsolete keys is a good approach. Most localization tools focus on missing content, but abandoned keys also create confusion for translators and make it harder to understand which copy is still used by the product.
The clearest takeaway is that progressive enhancement does not mean avoiding JavaScript—it means giving it the right responsibility. A working HTML form provides resilience, while JavaScript improves speed, focus management, and presentation without becoming the only path to the result.
haleo
I like the idea of disabling enhancement after a failed request and allowing the next submission to use the browser’s native form behavior. That is a practical fallback and avoids trapping visitors inside a JavaScript error state.