fix(recipes/i18n): update code snippet to use collection id (withastro#11549)

Co-authored-by: Yan <[email protected]>

Author: ArmandPhilippot

src/content/docs/en/recipes/i18n.mdx

@@ -120,7 +120,7 @@ If you prefer the default language to not be visible in the URL unlike other lan
           const pages = await getCollection('blog');
 
           const paths = pages.map(page => {
-            const [lang, ...slug] = page.slug.split('/');
+            const [lang, ...slug] = page.id.split('/');
             return { params: { lang, slug: slug.join('/') || undefined }, props: page };
           });