i18n: add session language command

README.md

@@ -96,6 +96,7 @@ Ctrl+C     - Exit chat
 :search <keyword>    - Search full message history (case-insensitive)
 :mute-joins          - Toggle join/leave system notifications
 :support             - Show quick support guide
+:lang <en|zh>        - Switch UI language for this session
 :help                - Show available commands
 :clear               - Clear command output
 :q, :quit, :exit     - Disconnect

docs/CHANGELOG.md

@@ -6,6 +6,8 @@
 - Added a first i18n boundary: `TNT_LANG` / locale detection now chooses the
   default interactive UI language (`en` or `zh`) for username prompts, status
   hints, help language, and `:support`.
+- Added `:lang <en|zh>` so users can switch the interactive UI language for
+  their current session.
 
 ### Changed
 - NORMAL mode now opens at the latest visible messages instead of the oldest

include/i18n.h

@@ -13,6 +13,7 @@ typedef enum {
     I18N_NORMAL_NEW_MESSAGES
 } i18n_text_id_t;
 
+bool i18n_try_parse_lang(const char *value, help_lang_t *lang);
 help_lang_t i18n_parse_lang(const char *value, help_lang_t fallback);
 help_lang_t i18n_default_lang(void);
 const char *i18n_lang_code(help_lang_t lang);

src/commands.c

@@ -8,6 +8,7 @@
 #include "chat_room.h"
 #include "client.h"
 #include "common.h"
+#include "i18n.h"
 #include "message.h"
 #include "support.h"
 #include "tui.h"
@@ -82,7 +83,8 @@ static const char *suggest_command(const char *cmd) {
     static const char *commands[] = {
         "list", "users", "who", "nick", "name", "msg", "w", "inbox",
         "last", "search", "mute-joins", "mute", "support", "guide",
-        "help", "commands", "clear", "cls", "q", "quit", "exit"
+        "lang", "language", "help", "commands", "clear", "cls",
+        "q", "quit", "exit"
     };
     const char *best = NULL;
     int best_distance = 99;
@@ -177,6 +179,7 @@ void commands_dispatch(client_t *client) {
                        "search <keyword>    - Search message history\n"
                        "mute-joins          - Toggle join/leave notices\n"
                        "support             - Show quick support guide\n"
+                       "lang [en|zh]        - Show or switch UI language\n"
                        "help, commands      - Show this help\n"
                        "clear, cls          - Clear command output\n"
                        "q, quit, exit       - Disconnect\n"
@@ -191,6 +194,34 @@ void commands_dispatch(client_t *client) {
         support_append_interactive_panel(output, sizeof(output), &pos,
                                          client->help_lang);
 
+    } else if (strcmp(cmd, "lang") == 0 || strcmp(cmd, "language") == 0 ||
+               strncmp(cmd, "lang ", 5) == 0 ||
+               strncmp(cmd, "language ", 9) == 0) {
+        char *arg = NULL;
+        help_lang_t next_lang;
+
+        if (strncmp(cmd, "lang ", 5) == 0) {
+            arg = cmd + 5;
+        } else if (strncmp(cmd, "language ", 9) == 0) {
+            arg = cmd + 9;
+        }
+
+        if (!arg || arg[0] == '\0') {
+            buffer_appendf(output, sizeof(output), &pos,
+                           "Current language: %s\n"
+                           "Usage: lang <en|zh>\n",
+                           i18n_lang_code(client->help_lang));
+        } else if (i18n_try_parse_lang(arg, &next_lang)) {
+            client->help_lang = next_lang;
+            buffer_appendf(output, sizeof(output), &pos,
+                           "Language set to: %s\n",
+                           i18n_lang_code(client->help_lang));
+        } else {
+            buffer_appendf(output, sizeof(output), &pos,
+                           "Unsupported language: %s\n"
+                           "Usage: lang <en|zh>\n", arg);
+        }
+
     } else if (strncmp(cmd, "msg ", 4) == 0 || strncmp(cmd, "w ", 2) == 0) {
         char *rest = (cmd[0] == 'w') ? cmd + 2 : cmd + 4;
         while (*rest == ' ') rest++;

src/i18n.c

@@ -17,23 +17,33 @@ static bool starts_with_lang(const char *value, const char *prefix) {
     return *value == '\0' || *value == '_' || *value == '-' || *value == '.';
 }
 
-help_lang_t i18n_parse_lang(const char *value, help_lang_t fallback) {
+bool i18n_try_parse_lang(const char *value, help_lang_t *lang) {
     if (!value || value[0] == '\0') {
-        return fallback;
+        return false;
     }
 
     if (starts_with_lang(value, "zh") ||
         starts_with_lang(value, "cn") ||
         starts_with_lang(value, "chinese")) {
-        return LANG_ZH;
+        if (lang) *lang = LANG_ZH;
+        return true;
     }
 
     if (starts_with_lang(value, "en") ||
         starts_with_lang(value, "c") ||
         starts_with_lang(value, "posix")) {
-        return LANG_EN;
+        if (lang) *lang = LANG_EN;
+        return true;
     }
 
+    return false;
+}
+
+help_lang_t i18n_parse_lang(const char *value, help_lang_t fallback) {
+    help_lang_t lang;
+    if (i18n_try_parse_lang(value, &lang)) {
+        return lang;
+    }
     return fallback;
 }
 

src/tui.c

@@ -784,6 +784,7 @@ const char* tui_get_help_text(help_lang_t lang) {
                "  :search <keyword>    - Search message history\n"
                "  :mute-joins          - Toggle join/leave notices\n"
                "  :support             - Show quick support guide\n"
+               "  :lang <en|zh>        - Switch UI language\n"
                "  :help                - Show available commands\n"
                "  :clear               - Clear command output\n"
                "  :q, :quit, :exit     - Disconnect\n"
@@ -838,6 +839,7 @@ const char* tui_get_help_text(help_lang_t lang) {
                "  :search <关键词>     - 搜索消息历史\n"
                "  :mute-joins          - 切换加入/离开提示\n"
                "  :support             - 显示快速支持指南\n"
+               "  :lang <en|zh>        - 切换界面语言\n"
                "  :help                - 显示可用命令\n"
                "  :clear               - 清空命令输出\n"
                "  :q, :quit, :exit     - 断开连接\n"

tests/test_interactive_input.sh

@@ -148,6 +148,13 @@ send -- "support\r"
 expect "支持"
 expect "Press any key"
 send -- "q"
+expect "NORMAL"
+send -- ":"
+expect ":"
+send -- "lang en\r"
+expect "Language set to: en"
+expect "Press any key"
+send -- "q"
 sleep 0.2
 send -- "\003"
 sleep 0.2

tests/unit/test_i18n.c

@@ -17,11 +17,19 @@
 static int tests_passed = 0;
 
 TEST(parse_explicit_languages) {
+    help_lang_t lang;
+
     assert(i18n_parse_lang("zh", LANG_EN) == LANG_ZH);
     assert(i18n_parse_lang("zh_CN.UTF-8", LANG_EN) == LANG_ZH);
     assert(i18n_parse_lang("cn", LANG_EN) == LANG_ZH);
     assert(i18n_parse_lang("en", LANG_ZH) == LANG_EN);
     assert(i18n_parse_lang("en_US.UTF-8", LANG_ZH) == LANG_EN);
+
+    assert(i18n_try_parse_lang("zh", &lang) == true);
+    assert(lang == LANG_ZH);
+    assert(i18n_try_parse_lang("en", &lang) == true);
+    assert(lang == LANG_EN);
+    assert(i18n_try_parse_lang("fr", &lang) == false);
 }
 
 TEST(parse_unknown_uses_fallback) {

tnt.1

@@ -121,6 +121,7 @@ l l.
 :search \fIkeyword\fR	Case\-insensitive search across full message history
 :mute\-joins	Toggle join/leave system notifications on/off
 :support	Show quick support guide
+:lang \fIen|zh\fR	Switch UI language for this session
 :help	Show available commands
 :clear	Clear command output
 :q, :quit, :exit	Disconnect