Add L10n (#39)

Have all localisation components at one place.

Sources/FoundationExtensions/L10n/.sourcery-l10n-example.yml

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+sources:
+  include:
+    - Sources/FooBar/Extensions/L10n.swift
+  exclude:
+    - Sources/FooBar/Generated
+templates:
+  - ../Tools/Sourcery/Templates/Localizable.stencil
+output:
+  Sources/FooBar/Generated
+args:
+  imports: ["Foundation"]
+  testable-imports: []

Sources/FoundationExtensions/L10n/L10n.swift

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+// Copyright © 2022 Lautsprecher Teufel GmbH. All rights reserved.
+
+import Foundation
+
+/**
+ Type-safe localization in 3 easy steps ✨.
+
+ **Step 1**: Define your strings in an extension of L10n (i.e. in `App/Sources/L10n/L10n.swift`).
+
+ ```
+ extension L10n {
+     public enum HomeScreen: Localizable {
+         // sourcery: comment=Navigation Bar Title on Home screen
+         case navigationBarTitle
+
+         // sourcery: comment=Some value with parameters
+         case value(/* sourcery: format=%d */ count: Int, another: String, /* sourcery: format=%.2f */ exacly: Float)
+
+         // sourcery: comment=Title for submit button on Home screen
+         case submitButton
+     }
+ }
+ ```
+
+ **Step 2**: Use [sourcery](https://github.com/krzysztofzablocki/Sourcery) + genstrings + [MergeL10n](https://github.com/teufelaudio/MergeL10n) to generate `Localizable.strings`.
+ See .sourcery-l10n-example.yml and adjust the paths to your project. The sourcery template
+ can be found in `Tools/Sourcery/Templates/Sources/Localizable.stencil`.
+
+
+ ```
+ # Makefile excerpt
+ App/Sources/Generated/Localizable.generated.swift: App/Sources/L10n/L10n.swift
+     sourcery --config App/Sources/.sourcery-l10n.yml
+     genstrings -o App/Sources/Resources/zz.lproj -s LS App/Sources/Generated/Localizable.generated.swift
+     Tools/MergeL10n pseudo-to-languages --base-paths="App/Sources/Resources"
+
+ ```
+
+ **Step 3**: Refer to the strings with the `.localizedString` method.
+
+ ```
+ public struct Example: View {
+     public var body: some View {
+         Text(L10n.HomeScreen.navigationBarTitle.localizedString)
+     }
+ }
+ ```
+ */
+public enum L10n {
+}

Sources/FoundationExtensions/L10n/Localizable.swift

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+// Copyright © 2022 Lautsprecher Teufel GmbH. All rights reserved.
+
+import SwiftUI
+
+@available(iOS 13.0, *)
+public protocol Localizable {
+    var key: LocalizedStringKey { get }
+    var rootKey: String { get }
+}
+
+@available(iOS 13.0, *)
+extension Localizable {
+    public var key: LocalizedStringKey {
+        .init(
+            "\(rootKey).\(Mirror(reflecting: self).children.first?.label ?? "\(self)")"
+        )
+    }
+
+    public var rootKey: String {
+        String(reflecting: Self.self)
+    }
+}