Implemented the "localisation(for:)" function of the Bundle+LocalisationBundle extension for the Core library.

Sources/Core/Errors/BundleError.swift

@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftLibs open source project
+//
+// Copyright (c) 2023 Röck+Cöde VoF. and the SwiftLibs project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftLibs project authors
+//
+//===----------------------------------------------------------------------===//
+
+public enum BundleError: Error {
+    case bundleNotFound
+}