feat: Add i18n support

ExampleI18n/.gitignore

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+.DS_Store
+/.build
+/Packages
+/*.xcodeproj
+xcuserdata/
+deploy

ExampleI18n/Package.swift

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+// swift-tools-version:6.0
+
+import PackageDescription
+
+let package = Package(
+  name: "ExampleI18n",
+  platforms: [
+    .macOS(.v14),
+  ],
+  dependencies: [
+    .package(path: "../"),
+    .package(url: "https://github.com/loopwerk/SagaParsleyMarkdownReader", from: "1.0.0"),
+    .package(url: "https://github.com/loopwerk/SagaSwimRenderer", from: "1.0.0"),
+  ],
+  targets: [
+    .executableTarget(
+      name: "ExampleI18n",
+      dependencies: [
+        "Saga",
+        "SagaParsleyMarkdownReader",
+        "SagaSwimRenderer",
+      ]
+    ),
+  ]
+)

ExampleI18n/Sources/ExampleI18n/main.swift

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+import Foundation
+import Saga
+import SagaParsleyMarkdownReader
+import SagaPathKit
+import SagaSwimRenderer
+
+enum SiteMetadata {
+  static let url = URL(string: "http://www.example.com")!
+  static let name = "i18n Example"
+  static let author = "Kevin Renskers"
+}
+
+struct ArticleMetadata: Metadata {
+  let tags: [String]
+}
+
+try await Saga(input: "content", output: "deploy")
+  .i18n(locales: ["en", "nl"], defaultLocale: "en")
+
+  // Articles with list and tag pages
+  .register(
+    folder: "articles",
+    metadata: ArticleMetadata.self,
+    readers: [.parsleyMarkdownReader],
+    writers: [
+      .itemWriter(swim(renderArticle)),
+      .listWriter(swim(renderArticles)),
+      .tagWriter(swim(renderTag), tags: \.metadata.tags),
+    ]
+  )
+
+  // All remaining markdown files (index, about)
+  .register(
+    metadata: EmptyMetadata.self,
+    readers: [.parsleyMarkdownReader],
+    writers: [.itemWriter(swim(renderPage))]
+  )
+
+  // Sitemap
+  .createPage("sitemap.xml", using: Saga.sitemap(baseURL: SiteMetadata.url))
+
+  .run()

ExampleI18n/Sources/ExampleI18n/templates.swift

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+import Foundation
+import HTML
+import Saga
+import SagaPathKit
+import SagaSwimRenderer
+
+// MARK: - Translations
+
+func t(_ key: String, locale: String) -> String {
+  let strings: [String: [String: String]] = [
+    "en": [
+      "articles": "Articles",
+      "about": "About",
+      "home": "Home",
+      "tagged": "Tagged",
+      "read_more": "Read more",
+      "built_with": "Built with",
+    ],
+    "nl": [
+      "articles": "Artikelen",
+      "about": "Over ons",
+      "home": "Home",
+      "tagged": "Getagd",
+      "read_more": "Lees meer",
+      "built_with": "Gebouwd met",
+    ],
+  ]
+  return strings[locale]?[key] ?? key
+}
+
+// MARK: - Language switcher
+
+func languageSwitcher(currentLocale: String, item: AnyItem) -> Node {
+  nav(class: "lang-switcher") {
+    if currentLocale == "en" {
+      span(class: "active") { "EN" }
+    } else {
+      if let enVersion = item.translations["en"] {
+        a(href: enVersion.url) { "EN" }
+      }
+    }
+
+    if currentLocale == "nl" {
+      span(class: "active") { "NL" }
+    } else {
+      if let nlVersion = item.translations["nl"] {
+        a(href: nlVersion.url) { "NL" }
+      }
+    }
+  }
+}
+
+// MARK: - Base layout
+
+func baseHtml(title pageTitle: String, locale: String, @NodeBuilder children: () -> NodeConvertible) -> Node {
+  let articlesPath = locale == "en" ? "/articles/" : "/nl/articles/"
+  let aboutPath = locale == "en" ? "/about/" : "/nl/over-ons/"
+  let homePath = locale == "en" ? "/" : "/nl/"
+
+  return html(lang: locale) {
+    head {
+      meta(charset: "utf-8")
+      meta(content: "width=device-width, initial-scale=1", name: "viewport")
+      title { SiteMetadata.name + ": " + pageTitle }
+      link(href: "/static/style.css", rel: "stylesheet")
+    }
+    body {
+      header {
+        nav {
+          a(class: "site-title", href: homePath) { SiteMetadata.name }
+          div(class: "nav-links") {
+            a(href: homePath) { t("home", locale: locale) }
+            a(href: articlesPath) { t("articles", locale: locale) }
+            a(href: aboutPath) { t("about", locale: locale) }
+          }
+        }
+      }
+      main {
+        children()
+      }
+      footer {
+        p {
+          t("built_with", locale: locale)
+          " "
+          a(href: "https://github.com/loopwerk/Saga") { "Saga" }
+        }
+      }
+    }
+  }
+}
+
+// MARK: - Articles
+
+func renderArticle(context: ItemRenderingContext<ArticleMetadata>) -> Node {
+  let locale = context.locale ?? "en"
+  let tagBase = locale == "en" ? "/articles/tag" : "/nl/articles/tag"
+
+  return baseHtml(title: context.item.title, locale: locale) {
+    languageSwitcher(currentLocale: locale, item: context.item)
+
+    h1 { context.item.title }
+    ul(class: "tags") {
+      context.item.metadata.tags.map { tag in
+        li {
+          a(href: "\(tagBase)/\(tag.slugified)/") { tag }
+        }
+      }
+    }
+    div(class: "article-body") {
+      Node.raw(context.item.body)
+    }
+  }
+}
+
+func renderArticles(context: ItemsRenderingContext<ArticleMetadata>) -> Node {
+  let locale = context.locale ?? "en"
+
+  return baseHtml(title: t("articles", locale: locale), locale: locale) {
+    h1 { t("articles", locale: locale) }
+    context.items.map { article in
+      div(class: "article-card") {
+        a(href: article.url) { article.title }
+      }
+    }
+  }
+}
+
+func renderTag(context: PartitionedRenderingContext<String, ArticleMetadata>) -> Node {
+  let locale = context.locale ?? "en"
+
+  return baseHtml(title: "\(t("tagged", locale: locale)): \(context.key)", locale: locale) {
+    h1 { "\(t("tagged", locale: locale)): \(context.key)" }
+    context.items.map { article in
+      div(class: "article-card") {
+        a(href: article.url) { article.title }
+      }
+    }
+  }
+}
+
+// MARK: - Generic pages
+
+func renderPage(context: ItemRenderingContext<EmptyMetadata>) -> Node {
+  let locale = context.locale ?? "en"
+
+  return baseHtml(title: context.item.title, locale: locale) {
+    languageSwitcher(currentLocale: locale, item: context.item)
+
+    div(class: "page") {
+      h1 { context.item.title }
+      div(class: "article-body") {
+        Node.raw(context.item.body)
+      }
+    }
+  }
+}

ExampleI18n/content/en/about.md

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+---
+slug: about
+---
+# About this site
+This is an example site demonstrating Saga's internationalization support. Content is organized in locale folders (`en/`, `nl/`) and Saga handles translation linking and per-locale output automatically.

ExampleI18n/content/en/articles/getting-started.md

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+---
+tags: tutorial
+date: 2024-07-01
+---
+# Getting Started with Saga
+To create a multilingual site with Saga, start by organizing your content into locale folders. Then configure i18n before your register calls:
+
+```swift
+try await Saga(input: "content", output: "deploy")
+  .i18n(locales: ["en", "nl"], defaultLocale: "en")
+  .register(...)
+  .run()
+```
+
+Your writers automatically run per-locale, so list pages, tag pages, and feeds are all generated separately for each language.

ExampleI18n/content/en/articles/hello-world.md

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+---
+tags: news, welcome
+date: 2024-06-15
+---
+# Hello World
+Welcome to our multilingual blog! This is our very first article, available in both English and Dutch.
+
+Saga makes it easy to build sites that serve content in multiple languages. Each locale gets its own folder, and translations are linked automatically by matching filenames.

ExampleI18n/content/en/index.md

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+# Welcome
+This is an example multilingual site built with Saga. It supports English and Dutch.
+
+Check out the [articles](/articles/) or read more [about this site](/about/).

ExampleI18n/content/nl/about.md

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+---
+slug: over-ons
+---
+# Over deze site
+Dit is een voorbeeldsite die de internationalisatie-ondersteuning van Saga demonstreert. Content is georganiseerd in taalspecifieke mappen (`en/`, `nl/`) en Saga koppelt vertalingen automatisch aan elkaar.

ExampleI18n/content/nl/articles/getting-started.md

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+---
+tags: handleiding
+date: 2024-07-01
+---
+# Aan de slag met Saga
+Om een meertalige site te maken met Saga, begin je met het organiseren van je content in taalmappen. Configureer daarna i18n voor je register-aanroepen:
+
+```swift
+try await Saga(input: "content", output: "deploy")
+  .i18n(locales: ["en", "nl"], defaultLocale: "en")
+  .register(...)
+  .run()
+```
+
+Je writers draaien automatisch per taal, dus lijstpagina's, tagpagina's en feeds worden allemaal apart gegenereerd voor elke taal.

ExampleI18n/content/nl/articles/hello-world.md

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+---
+tags: nieuws, welkom
+date: 2024-06-15
+---
+# Hallo Wereld
+Welkom op onze meertalige blog! Dit is ons allereerste artikel, beschikbaar in zowel Engels als Nederlands.
+
+Saga maakt het eenvoudig om sites te bouwen die content in meerdere talen aanbieden. Elke taal krijgt zijn eigen map, en vertalingen worden automatisch gekoppeld op basis van bestandsnamen.

ExampleI18n/content/nl/index.md

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+# Welkom
+Dit is een voorbeeld meertalige site gebouwd met Saga. De site ondersteunt Engels en Nederlands.
+
+Bekijk de [artikelen](/nl/articles/) of lees meer [over deze site](/nl/over-ons/).