Add i18n support, language toggle UI, and translate Settings dialog (#334)

* i18n support added

* fix: align i18n implementation with Next.js 16 guide

- Rename middleware.ts to proxy.ts (Next.js 16 convention)
- Fix params type to Promise<{lang: string}> for layout/metadata
- Add 'server-only' directive and dynamic imports to dictionaries.ts
- Add hasLocale type guard and notFound() for invalid locales
- Wrap LanguageToggle in Suspense for useSearchParams
- Fix dictionary key mismatch (learnmore -> learnMore)
- Improve Chinese translations per Gemini review:
  - loading ellipsis, new -> 新建, styledMode -> 精致
  - goodResponse/badResponse -> 有帮助/无帮助
  - closeProtection -> 关闭确认, fileExceeds phrasing
- Improve Japanese translations per Gemini review:
  - closeProtection -> ページ離脱確認
  - invalidAccessCode phrasing, appendDiagram -> に追加
  - styledMode -> スタイル付き

---------

Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

app/[lang]/layout.tsx

@@ -0,0 +1,172 @@
+import { GoogleAnalytics } from "@next/third-parties/google"
+import type { Metadata, Viewport } from "next"
+import { JetBrains_Mono, Plus_Jakarta_Sans } from "next/font/google"
+import { notFound } from "next/navigation"
+import { DiagramProvider } from "@/contexts/diagram-context"
+import { DictionaryProvider } from "@/hooks/use-dictionary"
+import type { Locale } from "@/lib/i18n/config"
+import { i18n } from "@/lib/i18n/config"
+import { getDictionary, hasLocale } from "@/lib/i18n/dictionaries"
+
+import "../globals.css"
+
+const plusJakarta = Plus_Jakarta_Sans({
+    variable: "--font-sans",
+    subsets: ["latin"],
+    weight: ["400", "500", "600", "700"],
+})
+
+const jetbrainsMono = JetBrains_Mono({
+    variable: "--font-mono",
+    subsets: ["latin"],
+    weight: ["400", "500"],
+})
+
+export const viewport: Viewport = {
+    width: "device-width",
+    initialScale: 1,
+    maximumScale: 1,
+    userScalable: false,
+}
+
+// Generate static params for all locales
+export async function generateStaticParams() {
+    return i18n.locales.map((locale) => ({ lang: locale }))
+}
+
+// Generate metadata per locale
+export async function generateMetadata({
+    params,
+}: {
+    params: Promise<{ lang: string }>
+}): Promise<Metadata> {
+    const { lang: rawLang } = await params
+    const lang = (rawLang in { en: 1, zh: 1, ja: 1 } ? rawLang : "en") as Locale
+
+    // Default to English metadata
+    const titles: Record<Locale, string> = {
+        en: "Next AI Draw.io - AI-Powered Diagram Generator",
+        zh: "Next AI Draw.io - AI powered diagram generator",
+        ja: "Next AI Draw.io - AI-powered diagram generator",
+    }
+
+    const descriptions: Record<Locale, string> = {
+        en: "Create AWS architecture diagrams, flowcharts, and technical diagrams using AI. Free online tool integrating draw.io with AI assistance for professional diagram creation.",
+        zh: "Use AI to create AWS architecture diagrams, flowcharts, and technical diagrams. Free online tool integrated with draw.io and AI assistance for professional diagram creation.",
+        ja: "Create AWS architecture diagrams, flowcharts, and technical diagrams using AI. Create professional diagrams with a free online tool that integrates draw.io with an AI assistant.",
+    }
+
+    return {
+        title: titles[lang],
+        description: descriptions[lang],
+        keywords: [
+            "AI diagram generator",
+            "AWS architecture",
+            "flowchart creator",
+            "draw.io",
+            "AI drawing tool",
+            "technical diagrams",
+            "diagram automation",
+            "free diagram generator",
+            "online diagram maker",
+        ],
+        authors: [{ name: "Next AI Draw.io" }],
+        creator: "Next AI Draw.io",
+        publisher: "Next AI Draw.io",
+        metadataBase: new URL("https://next-ai-drawio.jiang.jp"),
+        openGraph: {
+            title: titles[lang],
+            description: descriptions[lang],
+            type: "website",
+            url: "https://next-ai-drawio.jiang.jp",
+            siteName: "Next AI Draw.io",
+            locale: lang === "zh" ? "zh_CN" : lang === "ja" ? "ja_JP" : "en_US",
+            images: [
+                {
+                    url: "/architecture.png",
+                    width: 1200,
+                    height: 630,
+                    alt: "Next AI Draw.io - AI-powered diagram creation tool",
+                },
+            ],
+        },
+        twitter: {
+            card: "summary_large_image",
+            title: titles[lang],
+            description: descriptions[lang],
+            images: ["/architecture.png"],
+        },
+        robots: {
+            index: true,
+            follow: true,
+            googleBot: {
+                index: true,
+                follow: true,
+                "max-video-preview": -1,
+                "max-image-preview": "large",
+                "max-snippet": -1,
+            },
+        },
+        icons: {
+            icon: "/favicon.ico",
+        },
+        alternates: {
+            languages: {
+                en: "/en",
+                zh: "/zh",
+                ja: "/ja",
+            },
+        },
+    }
+}
+
+export default async function RootLayout({
+    children,
+    params,
+}: Readonly<{
+    children: React.ReactNode
+    params: Promise<{ lang: string }>
+}>) {
+    const { lang } = await params
+    if (!hasLocale(lang)) notFound()
+    const validLang = lang as Locale
+    const dictionary = await getDictionary(validLang)
+
+    const jsonLd = {
+        "@context": "https://schema.org",
+        "@type": "SoftwareApplication",
+        name: "Next AI Draw.io",
+        applicationCategory: "DesignApplication",
+        operatingSystem: "Web Browser",
+        description:
+            "AI-powered diagram generator with targeted XML editing capabilities that integrates with draw.io for creating AWS architecture diagrams, flowcharts, and technical diagrams. Features diagram history, multi-provider AI support, and real-time collaboration.",
+        url: "https://next-ai-drawio.jiang.jp",
+        inLanguage: validLang,
+        offers: {
+            "@type": "Offer",
+            price: "0",
+            priceCurrency: "USD",
+        },
+    }
+
+    return (
+        <html lang={validLang} suppressHydrationWarning>
+            <head>
+                <script
+                    type="application/ld+json"
+                    dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
+                />
+            </head>
+            <body
+                className={`${plusJakarta.variable} ${jetbrainsMono.variable} antialiased`}
+            >
+                <DictionaryProvider dictionary={dictionary}>
+                    <DiagramProvider>{children}</DiagramProvider>
+                </DictionaryProvider>
+            </body>
+            {process.env.NEXT_PUBLIC_GA_ID && (
+                <GoogleAnalytics gaId={process.env.NEXT_PUBLIC_GA_ID} />
+            )}
+        </html>
+    )
+}

app/[lang]/page.tsx

@@ -108,16 +108,11 @@ export default function Home() {
     useEffect(() => {
         const checkMobile = () => {
             const newIsMobile = window.innerWidth < 768
-            // If crossing the breakpoint (not initial render), save diagram and reset draw.io
             if (
                 !isInitialRenderRef.current &&
                 newIsMobile !== isMobileRef.current
             ) {
-                // Save diagram before remounting (fire and forget)
-                saveDiagramToStorage().catch(() => {
-                    // Ignore timeout errors during resize
-                })
-                // Reset draw.io ready state so onLoad triggers again after remount
+                saveDiagramToStorage().catch(() => {})
                 resetDrawioReady()
             }
             isMobileRef.current = newIsMobile
@@ -177,7 +172,6 @@ export default function Home() {
                 direction={isMobile ? "vertical" : "horizontal"}
                 className="h-full"
             >
-                {/* Draw.io Canvas */}
                 <ResizablePanel
                     id="drawio-panel"
                     defaultSize={isMobile ? 50 : 67}

app/layout.tsx

@@ -1,125 +0,0 @@
-import { GoogleAnalytics } from "@next/third-parties/google"
-import type { Metadata, Viewport } from "next"
-import { JetBrains_Mono, Plus_Jakarta_Sans } from "next/font/google"
-import { DiagramProvider } from "@/contexts/diagram-context"
-
-import "./globals.css"
-
-const plusJakarta = Plus_Jakarta_Sans({
-    variable: "--font-sans",
-    subsets: ["latin"],
-    weight: ["400", "500", "600", "700"],
-})
-
-const jetbrainsMono = JetBrains_Mono({
-    variable: "--font-mono",
-    subsets: ["latin"],
-    weight: ["400", "500"],
-})
-
-export const viewport: Viewport = {
-    width: "device-width",
-    initialScale: 1,
-    maximumScale: 1,
-    userScalable: false,
-}
-
-export const metadata: Metadata = {
-    title: "Next AI Draw.io - AI-Powered Diagram Generator",
-    description:
-        "Create AWS architecture diagrams, flowcharts, and technical diagrams using AI. Free online tool integrating draw.io with AI assistance for professional diagram creation.",
-    keywords: [
-        "AI diagram generator",
-        "AWS architecture",
-        "flowchart creator",
-        "draw.io",
-        "AI drawing tool",
-        "technical diagrams",
-        "diagram automation",
-        "free diagram generator",
-        "online diagram maker",
-    ],
-    authors: [{ name: "Next AI Draw.io" }],
-    creator: "Next AI Draw.io",
-    publisher: "Next AI Draw.io",
-    metadataBase: new URL("https://next-ai-drawio.jiang.jp"),
-    openGraph: {
-        title: "Next AI Draw.io - AI Diagram Generator",
-        description:
-            "Create professional diagrams with AI assistance. Supports AWS architecture, flowcharts, and more.",
-        type: "website",
-        url: "https://next-ai-drawio.jiang.jp",
-        siteName: "Next AI Draw.io",
-        locale: "en_US",
-        images: [
-            {
-                url: "/architecture.png",
-                width: 1200,
-                height: 630,
-                alt: "Next AI Draw.io - AI-powered diagram creation tool",
-            },
-        ],
-    },
-    twitter: {
-        card: "summary_large_image",
-        title: "Next AI Draw.io - AI Diagram Generator",
-        description:
-            "Create professional diagrams with AI assistance. Free, no login required.",
-        images: ["/architecture.png"],
-    },
-    robots: {
-        index: true,
-        follow: true,
-        googleBot: {
-            index: true,
-            follow: true,
-            "max-video-preview": -1,
-            "max-image-preview": "large",
-            "max-snippet": -1,
-        },
-    },
-    icons: {
-        icon: "/favicon.ico",
-    },
-}
-
-export default function RootLayout({
-    children,
-}: Readonly<{
-    children: React.ReactNode
-}>) {
-    const jsonLd = {
-        "@context": "https://schema.org",
-        "@type": "SoftwareApplication",
-        name: "Next AI Draw.io",
-        applicationCategory: "DesignApplication",
-        operatingSystem: "Web Browser",
-        description:
-            "AI-powered diagram generator with targeted XML editing capabilities that integrates with draw.io for creating AWS architecture diagrams, flowcharts, and technical diagrams. Features diagram history, multi-provider AI support, and real-time collaboration.",
-        url: "https://next-ai-drawio.jiang.jp",
-        offers: {
-            "@type": "Offer",
-            price: "0",
-            priceCurrency: "USD",
-        },
-    }
-
-    return (
-        <html lang="en" suppressHydrationWarning>
-            <head>
-                <script
-                    type="application/ld+json"
-                    dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
-                />
-            </head>
-            <body
-                className={`${plusJakarta.variable} ${jetbrainsMono.variable} antialiased`}
-            >
-                <DiagramProvider>{children}</DiagramProvider>
-            </body>
-            {process.env.NEXT_PUBLIC_GA_ID && (
-                <GoogleAnalytics gaId={process.env.NEXT_PUBLIC_GA_ID} />
-            )}
-        </html>
-    )
-}