[Enhancement] String localisation (#21)

This PR contains the work done to provide string localisation support for the `Core` library.

To provide further details about the work done:
- [x] implemented the `localisation(for:)` function for the `Bundle+LocalisationBundle` extension;
- [x] implemented the `localise(for: in: value: table:)` function for the `String+Localisation` extension;
- [x] defined English as the default localisation language in the `Package.swift` file;
- [x] added the "vscode" target to the `Makefile` file.

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: #21

Sources/Core/Extensions/Bundle+LocalisationBundle.swift

@@ -0,0 +1,42 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+
+public extension Bundle {
+    
+    // MARK: Functions
+    
+    /// Retrieve a localisation bundle for a given language code or identifier, if exist inside a certain bundle.
+    /// - Parameter languageCode: A string that represent a language code or identifier.
+    /// - Returns: A `Bundle` instance that contains localised resources based on a given language code or identifier.
+    /// - Throws: A `BundleError` error in case the localisation bundle for a given language code  or identifier is not found inside a certain bundle.
+    func localisation(for languageCode: String) throws -> Bundle {
+        guard
+            let path = path(forResource: languageCode, ofType: .ResourceType.localisationBundle),
+            let bundle = Bundle(path: path)
+        else {
+            throw BundleError.bundleNotFound
+        }
+        
+        return bundle
+    }
+
+}
+
+// MARK: - String+Constants
+
+private extension String {
+    enum ResourceType {
+        static let localisationBundle = "lproj"
+    }
+}

Sources/Core/Extensions/String+Localisation.swift

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+
+public extension String {
+    
+    // MARK: Functions
+    
+    /// Localise a string based on a given language code or identifier in an specific bundle.
+    /// - Parameters:
+    ///   - languageCode: A string that represent a language code or identifier.
+    ///   - bundle: A bundle in which to retrieve a localisation bundle.
+    ///   - value: A default value to return if key is nil or if a localized string for key can't be found in the table.
+    ///   - table: The receiver's string table to search. In case of nil or an empty string, the method attempts to use the table in `Localizable.strings`.
+    /// - Returns: A localized version of the string in case it is found. Otherwise, it returns the original string or a default string, if provided.
+    func localise(
+        for languageCode: String,
+        in bundle: Bundle,
+        value: String? = nil,
+        table: String? = nil
+    ) -> String {
+        do {
+            return try bundle
+                .localisation(for: languageCode)
+                .localizedString(
+                    forKey: self,
+                    value: value,
+                    table: table
+                )
+        } catch {
+            return value ?? self
+        }
+    }
+    
+}