Fix links to external pages

Sources/Generator/Content/Element.swift

@@ -289,16 +289,23 @@ struct Element {
         self.readElements(in: folder, source: path, log: log)
     }
 
-    func getContainedIds(log: MetadataInfoLogger) -> [String : String] {
-        elements.reduce(into: [id : path]) { dict, element in
-            element.getContainedIds(log: log).forEach { id, path in
-                if let existing = dict[id] {
-                    log.error("Conflicting id with \(existing)", source: path)
-                } else {
-                    dict[id] = path
-                }
+    func getExternalPageMap(language: String) -> [String : String] {
+        var result = [String : String]()
+        if let ext = getExternalLink(for: language) {
+            result[id] = ext
+        } else {
+            result[id] = path + Element.htmlPagePathAddition(for: language)
+        }
+        elements.forEach { element in
+            element.getExternalPageMap(language: language).forEach { key, value in
+                result[key] = value
             }
         }
+        return result
+    }
+
+    private func getExternalLink(for language: String) -> String? {
+        languages.first { $0.language == language }?.externalUrl
     }
 }
 
@@ -381,6 +388,9 @@ extension Element {
      - Returns: The relative url from a localized page of the element to the target file.
      */
     func relativePathToOtherSiteElement(file: String) -> String {
+        guard !file.hasPrefix("/") else {
+            return file
+        }
         // Note: The element `path` is missing the last component
         // i.e. travel/alps instead of travel/alps/en.html
         let ownParts = path.components(separatedBy: "/")