Updated the LocalizationMiddleware middleware in the Infrastructure package to read explicit language requests.

Packages/Infrastructure/Tests/Cases/Public/Middlewares/LocalizationMiddlewareTests.swift

@@ -25,6 +25,9 @@ struct LocalizationMiddlewareTests {
         router.get("language") { _, context in
             context.language
         }
+        router.get("de/language") { _, context in
+            context.language
+        }
 
         return router
     }())
@@ -69,4 +72,44 @@ struct LocalizationMiddlewareTests {
         }
     }
 
+    @Test
+    func `honours a supported lang query parameter over the header`() async throws {
+        try await app.test(.router) { client in
+            try await client.execute(
+                uri: "/language?lang=de",
+                method: .get,
+                headers: [.acceptLanguage: "en"]
+            ) { response in
+                #expect(String(buffer: response.body) == "de")
+            }
+        }
+    }
+
+    /// A language's whole URL prefix answers in its language, so its not-found page does too.
+    @Test
+    func `pins the language a leading path segment names over the header`() async throws {
+        try await app.test(.router) { client in
+            try await client.execute(
+                uri: "/de/language",
+                method: .get,
+                headers: [.acceptLanguage: "en"]
+            ) { response in
+                #expect(String(buffer: response.body) == "de")
+            }
+        }
+    }
+
+    @Test
+    func `negotiates the header when the lang query parameter is unsupported`() async throws {
+        try await app.test(.router) { client in
+            try await client.execute(
+                uri: "/language?lang=fr",
+                method: .get,
+                headers: [.acceptLanguage: "de"]
+            ) { response in
+                #expect(String(buffer: response.body) == "de")
+            }
+        }
+    }
+
 }