Switching language leads to a “page not found” error

Using a translation plugin?

• Check that the same languages are ticked in both plugins, with the same default language.
• Check that the page is translated in that language. For untranslated pages, your translation plugin decides where the link goes.
• Re-save your permalinks: Settings → Permalinks → Save Changes.

Using built-in URLs (no translation plugin)? The plugin builds links like /fr/about/ but does not create those pages. Make sure each page exists at that address in every enabled language (see Built-in URLs without a translation plugin). If your pages live at other addresses, use the cls_pro_language_urls filter.

The top bar of the settings screen shows which URL source the plugin uses (for example WPML or Built-in URLs). If it says Built-in URLs but you use a translation plugin, that plugin is not active or not supported.