Fixes for the Localization package (#26)

This PR contains the work done to

Reviewed-on: rock-n-code/loud-amsterdam#26
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Packages/Localization/Tests/Utils/Resolvers/StubCatalog.swift

@@ -0,0 +1,23 @@
+import Foundation
+
+@testable import Localization
+
+/// A ``CatalogResolving`` backend with fixed languages, for exercising types apart from a bundled catalog.
+struct StubCatalog: CatalogResolving {
+
+    // MARK: Properties
+
+    let sourceLanguage: String
+    let languages: Set<String>
+    var state: CatalogState = .loaded
+
+    // MARK: Methods
+
+    func string(
+        for key: String,
+        in locale: Locale
+    ) -> String {
+        key
+    }
+
+}