feat(web): add Simplified Chinese (zh-CN) UI locale

CHANGELOG.md

@@ -7,6 +7,9 @@ Versioning: [Semantic Versioning](https://semver.org/spec/v2.0.0.html)
 
 ## [Unreleased]
 
+### Added
+- **Web UI Simplified Chinese.** The session viewer chrome — nav, sidebar, project/session lists, search, settings, memory, insights, session dock, info panel, 404 — is translated. Pick 中文 in the language switcher, pass `?lang=zh-CN`, set `locale: zh-CN` in `~/.config/ccx/config.yaml`, or let `Accept-Language` choose. English stays the default. Traditional Chinese is not a catalog yet.
+
 ## [0.18.0] - 2026-10-17
 
 ### Added

CLAUDE.md

@@ -64,6 +64,7 @@ ccx/
     parser/               JSONL parsing + tree building
     render/               Output formats (HTML, MD, Org, JSON)
     web/                  HTTP server + embedded templates
+    i18n/                 Web UI catalogs (en, zh-CN)
     db/                   SQLite persistence (stars)
     config/               CLAUDE_CODE_HOME logic
 ```

CONTRIBUTING.md

@@ -37,6 +37,7 @@ internal/
 ├── parser/              JSONL parsing + tree building
 ├── render/              Output formats (HTML, MD, Org)
 ├── web/                 HTTP server + templates
+├── i18n/                Web UI catalogs (en, zh-CN)
 ├── db/                  SQLite persistence (stars, cache)
 └── config/              Configuration paths
 ```

README.md

@@ -100,6 +100,7 @@ ccx doctor                       # Check setup
 ```yaml
 # ~/.config/ccx/config.yaml
 theme: dark
+locale: auto             # auto | en | zh-CN
 show_thinking: collapsed
 default_format: html
 providers:

docs/devlog/2026-09-21-web-i18n-zh.org

@@ -0,0 +1,60 @@
+* [2026-09-21] Dev Log: Web UI Simplified Chinese :WEB:I18N:
+
+** Context
+The web UI was English-only: chrome lived as string literals in
+=internal/web/templates.go= and friends. The user asked to finish
+multilingual support, specifically Chinese.
+
+** Why
+A Chinese-speaking operator should be able to browse projects,
+sessions, search, and the session dock without translating the
+chrome in their head. Session *content* stays as stored.
+
+** What
+- =FEAT= =internal/i18n= catalog: English is the source locale;
+  =zh-CN= covers the same keys. Tests fail on missing or empty
+  translations.
+- =FEAT= Language detection: =?lang==, =ccx-lang= cookie, config
+  =locale=, then =Accept-Language=. Default remains English.
+- =FEAT= Language switcher in the top nav (English / 简体中文).
+- =CHANGE= HTML =lang= and =window.CCX_I18N= so client JS uses the
+  same catalog.
+
+Traditional Chinese is not a catalog. CLI help is still English.
+
+** How
+Request-scoped =loc= translator. Top-level renderers are methods on
+=loc=; package-level wrappers keep English for existing tests that
+call them directly.
+
+** Decisions
+| Decision | Alternatives | Rationale | DRI | Timestamp |
+| Catalog maps in Go | gettext / x/text/message | Zero new deps; single binary | — | 2026-09-21 |
+| zh-CN only | Also zh-TW | No existing Traditional surface | — | 2026-09-21 |
+| Web UI first | Also CLI cobra help | CLI is not on the same catalog | — | 2026-09-21 |
+
+** Notes
+- =html.EscapeString= turns apostrophes into ='=. Catalog text
+  in element bodies uses a lighter escape so "Can't" stays readable.
+- =zh-TW= / =zh-Hant= do not fall through to Simplified Chinese.
+- Pages emit =translate="no"= and =google= =notranslate= so browser
+  auto-translate does not fight the in-app locale.
+
+** Review changes (2026-10-17, maintainers)
+Pushed onto this PR before merge; the notes above describe the PR as
+submitted.
+- =FIX= Browser translation stays on: no =translate="no"=, no
+  =notranslate= meta. They disabled it for every language ccx does not
+  ship, and for session transcripts.
+- =FIX= Accept-Language: any =en-*= region is English (=en-CA,zh;q=0.5=
+  picked Chinese), =zh-Hans-*= is Simplified, and =q=0= entries are
+  skipped as "not acceptable".
+- =FIX= The top-nav search API formats ages in the request's language.
+- =CHANGE= One detection path: =locFrom= detects; the middleware only
+  persists an explicit =?lang= as the cookie. The request-context
+  plumbing and the test-only English wrappers are gone.
+- =CHANGE= One escaper, =html.EscapeString=. Catalog values that carry
+  markup end in =_markup=, and a test holds every other value free of
+  =<=.
+- =CHANGE= Pages inline only the =js.*= keys client JS reads, not the
+  whole catalog. Nine unused keys removed.

internal/cmd/config.go

@@ -24,6 +24,7 @@ var configShowCmd = &cobra.Command{
 		fmt.Printf("claude_code_home: %s\n", config.ClaudeHome())
 		fmt.Printf("codex_home: %s\n", config.CodexHome())
 		fmt.Printf("theme: %s\n", config.Theme())
+		fmt.Printf("locale: %s\n", config.Locale())
 		fmt.Printf("rendering.syntax_highlight: %v\n", config.SyntaxHighlight())
 		fmt.Printf("rendering.show_thinking: %s\n", config.ShowThinking())
 		fmt.Printf("rendering.code_theme: %s\n", config.CodeTheme())
@@ -79,6 +80,7 @@ var configInitCmd = &cobra.Command{
 # codex_home: ~/.codex
 
 theme: dark              # dark | light | auto
+locale: auto             # auto | en | zh-CN
 
 rendering:
   syntax_highlight: true

internal/cmd/root.go

@@ -116,6 +116,7 @@ func initConfig() {
 	viper.SetDefault("codex_home", config.DefaultCodexHome())
 	viper.SetDefault("grok_home", config.DefaultGrokHome())
 	viper.SetDefault("theme", "dark")
+	viper.SetDefault("locale", "auto")
 	viper.SetDefault("rendering.syntax_highlight", true)
 	viper.SetDefault("rendering.show_thinking", "collapsed")
 	viper.SetDefault("rendering.code_theme", "monokai")

internal/config/config.go

@@ -65,6 +65,12 @@ func Theme() string {
 	return viper.GetString("theme")
 }
 
+// Locale is the configured UI language: auto, en, or zh-CN.
+// Empty and "auto" mean "detect from the request".
+func Locale() string {
+	return viper.GetString("locale")
+}
+
 func SyntaxHighlight() bool {
 	return viper.GetBool("rendering.syntax_highlight")
 }

internal/config/settings.go

@@ -8,6 +8,7 @@ type Settings struct {
 	GrokHome   string
 
 	Theme           string
+	Locale          string
 	SyntaxHighlight bool
 	ShowThinking    string
 	CodeTheme       string
@@ -54,6 +55,7 @@ func Load() *Settings {
 		CodexHome:       CodexHome(),
 		GrokHome:        GrokHome(),
 		Theme:           viper.GetString("theme"),
+		Locale:          viper.GetString("locale"),
 		SyntaxHighlight: viper.GetBool("rendering.syntax_highlight"),
 		ShowThinking:    viper.GetString("rendering.show_thinking"),
 		CodeTheme:       viper.GetString("rendering.code_theme"),

internal/i18n/detect.go

@@ -0,0 +1,101 @@
+package i18n
+
+import (
+	"net/http"
+	"strconv"
+	"strings"
+)
+
+// Detect picks a locale for an HTTP request.
+//
+// Precedence (most specific first):
+//  1. ?lang= query — explicit user action, also persisted as a cookie
+//  2. ccx-lang cookie — last explicit choice
+//  3. configured locale, when it is a real catalog (not auto/empty)
+//  4. Accept-Language
+//  5. English
+//
+// fromQuery is true only when the query param selected the locale,
+// so the caller can persist the cookie.
+func Detect(r *http.Request, configured string) (t *Translator, fromQuery bool) {
+	if r != nil {
+		if raw := strings.TrimSpace(r.URL.Query().Get(QueryParam)); raw != "" {
+			if code := Normalize(raw); code != "" {
+				return For(code), true
+			}
+		}
+		if c, err := r.Cookie(CookieName); err == nil && c.Value != "" {
+			if code := Normalize(c.Value); code != "" {
+				return For(code), false
+			}
+		}
+	}
+	if code := Normalize(configured); code != "" {
+		return For(code), false
+	}
+	if r != nil {
+		if code := matchAcceptLanguage(r.Header.Get("Accept-Language")); code != "" {
+			return For(code), false
+		}
+	}
+	return Default(), false
+}
+
+// matchAcceptLanguage walks a standard Accept-Language header and
+// returns the first tag we have a catalog for. q-values are honored
+// so "en;q=0.8, zh-CN;q=0.9" selects zh-CN.
+func matchAcceptLanguage(header string) string {
+	if header == "" {
+		return ""
+	}
+	type tagged struct {
+		code string
+		q    float64
+	}
+	var tags []tagged
+	for _, part := range strings.Split(header, ",") {
+		part = strings.TrimSpace(part)
+		if part == "" {
+			continue
+		}
+		name, rest, _ := strings.Cut(part, ";")
+		q := 1.0
+		rest = strings.TrimSpace(rest)
+		if strings.HasPrefix(rest, "q=") {
+			if v, err := strconv.ParseFloat(strings.TrimSpace(rest[2:]), 64); err == nil {
+				q = v
+			}
+		}
+		if q <= 0 {
+			continue // q=0 means "not acceptable"
+		}
+		code := Normalize(strings.TrimSpace(name))
+		if code == "" {
+			// Prefix match: zh-HK → no Traditional catalog, skip.
+			// zh → already handled by Normalize.
+			continue
+		}
+		tags = append(tags, tagged{code: code, q: q})
+	}
+	bestQ := -1.0
+	best := ""
+	for _, t := range tags {
+		if t.q > bestQ {
+			bestQ = t.q
+			best = t.code
+		}
+	}
+	return best
+}
+
+// Cookie builds the persistence cookie for an explicit language choice.
+func Cookie(code string) *http.Cookie {
+	return &http.Cookie{
+		Name:     CookieName,
+		Value:    Normalize(code),
+		Path:     "/",
+		MaxAge:   365 * 24 * 60 * 60,
+		SameSite: http.SameSiteLaxMode,
+		HttpOnly: false, // language switcher is a <select> in the page
+	}
+}