A visitor on a multilingual site clicks a link or menu item and lands on a page that has no version in the language they selected. What happens next shapes whether they stay or leave. The core problem is that the visitor needs a way to understand what went wrong and a visible path to continue browsing without having to rely on the browser back button or guess which link will take them somewhere useful.
One straightforward method is to show a short notice written in the visitor's chosen language, stating that the current page is not available in that language. Below the notice, provide two or three clear options: a link to the homepage in their language, a link to the nearest section or category page that does have a translation, and a link back to the page they came from. The notice itself should be brief and neutral in tone, not apologetic or overly long, so the visitor can scan it and act quickly.
A second approach is to display the content in a fallback language, usually the site's default language, while adding a persistent banner at the top of the page. The banner should say which language the content is actually shown in and offer a link to switch languages or return to the translated section. This works well when the untranslated page still contains useful information, such as a product listing or a reference table, and the visitor might prefer reading it in another language rather than seeing nothing at all.
Whichever method you choose, apply it consistently across the entire site. If some missing pages redirect silently, others show a notice, and still others display a blank layout, visitors cannot build a reliable mental model of how the site behaves. Pick one fallback pattern, document it in your site's style guide or content management rules, and check a sample of untranslated pages in each language to confirm the pattern holds. This check is something you can do by switching the site language and clicking through navigation links that you know have not been translated yet.