fixup! Render alternate representations as node variants

Sources/SwiftDocC/Model/Rendering/RenderNodeTranslator.swift

@@ -1852,21 +1852,30 @@ public struct RenderNodeTranslator: SemanticVisitor {
     private func variants(for documentationNode: DocumentationNode) -> [RenderNode.Variant] {
         let generator = PresentationURLGenerator(context: context, baseURL: bundle.baseURL)
 
-        var allVariants: [SourceLanguage: [ResolvedTopicReference]] = Dictionary(uniqueKeysWithValues: documentationNode.availableSourceLanguages.map { ($0, [identifier]) })
+        func mapSourceLanguageToVariants(identifier: ResolvedTopicReference, sourceLanguages: Set<SourceLanguage>) -> [(SourceLanguage, [ResolvedTopicReference])] {
+            sourceLanguages.map { ($0, [identifier]) }
+        }
+
+        var allVariants: [SourceLanguage: [ResolvedTopicReference]] = Dictionary(
+            mapSourceLanguageToVariants(identifier: identifier, sourceLanguages: documentationNode.availableSourceLanguages)
+        ) { value1, value2 in value1 + value2 }
 
         // Apply alternate representations
-        documentationNode.metadata?.alternateRepresentations.forEach { alternateRepresentation in
-            // Only counterparts which were able to be resolved to a reference should be included as an alternate representation.
-            // Unresolved counterparts can be ignored, as they would have been reported during link resolution.
-            guard case .resolved(.success(let counterpartReference)) = alternateRepresentation.reference else {
-                return
-            }
+        if let alternateRepresentations = documentationNode.metadata?.alternateRepresentations {
+            for alternateRepresentation in alternateRepresentations {
+                // Only alternate representations which were able to be resolved to a reference should be included as an alternate representation.
+                // Unresolved alternate representations can be ignored, as they would have been reported during link resolution.
+                guard case .resolved(.success(let alternateRepresentationReference)) = alternateRepresentation.reference else {
+                    continue
+                }
 
-            // Add all of the variants of the counterpart as additional variants for the current symbol
-            // If the current symbol and its counterpart share source languages, the list of variants for that language will contain multiple symbol references.
-            // Only the first symbol reference will be respected by Swift-DocC Render.
-            counterpartReference.sourceLanguages.forEach {
-                allVariants[$0, default: []].append(counterpartReference)
+                // Add the language representations of the alternate symbol as additional variants for the current symbol.
+                // Symbols can only specify custom alternate language representations for languages that the documented symbol doesn't already have a representation for.
+                // If the current symbol and its custom alternate representation share language representations, the custom language representation is ignored.
+                allVariants.merge(mapSourceLanguageToVariants(
+                    identifier: alternateRepresentationReference,
+                    sourceLanguages: alternateRepresentationReference.sourceLanguages
+                )) { value1, value2 in value1 }
             }
         }