core: let getPageTreePeers handle i18n (#2441)

* core: let  handle i18n

* core: replace extract from url

.changeset/cold-hoops-kiss.md

@@ -0,0 +1,5 @@
+---
+'fumadocs-core': patch
+---
+
+let `getPageTreePeers` handle i18n

packages/core/src/page-tree/utils.ts

@@ -68,15 +68,37 @@ export function getPageTreeRoots(
  * Get other page tree nodes that lives under the same parent
  */
 export function getPageTreePeers(
-  tree: PageTree.Root,
+  treeOrTrees: PageTree.Root | Record<string, PageTree.Root>,
   url: string,
 ): PageTree.Item[] {
-  const parent = findParentFromTree(tree, url);
-  if (!parent) return [];
+  // Check if it's a single tree or multiple trees (i18n)
+  if ('children' in treeOrTrees) {
+    // Single tree case
+    const tree = treeOrTrees as PageTree.Root;
+    const parent = findParentFromTree(tree, url);
+    if (!parent) return [];
 
-  return parent.children.filter(
-    (item) => item.type === 'page' && item.url !== url,
-  ) as PageTree.Item[];
+    return parent.children.filter(
+      (item) => item.type === 'page' && item.url !== url,
+    ) as PageTree.Item[];
+  }
+
+  // Multiple trees case
+  const trees = treeOrTrees as Record<string, PageTree.Root>;
+
+  for (const lang in trees) {
+    const rootTree = trees[lang];
+    if (rootTree) {
+      const parent = findParentFromTree(rootTree, url);
+      if (parent) {
+        return parent.children.filter(
+          (item) => item.type === 'page' && item.url !== url,
+        ) as PageTree.Item[];
+      }
+    }
+  }
+
+  return [];
 }
 
 function findParentFromTree(