diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 59478bb..5bd2048 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -33,6 +33,9 @@
   use the shared i18n table instead of inline command-flow conditionals.
 - Interactive and exec support guide copy now lives in a dedicated
   `support_text` module, with focused language-selection unit coverage.
+- Exec-mode help, usage errors, unknown-command feedback, and post validation
+  messages now follow `TNT_LANG` while preserving stable machine-readable
+  command output.
 
 ### Changed
 - NORMAL mode now opens at the latest visible messages instead of the oldest
diff --git a/include/i18n.h b/include/i18n.h
index 9d19e71..c7f1193 100644
--- a/include/i18n.h
+++ b/include/i18n.h
@@ -51,6 +51,14 @@ typedef enum {
     I18N_UNKNOWN_COMMAND_FORMAT,
     I18N_DID_YOU_MEAN_FORMAT,
     I18N_UNKNOWN_GUIDANCE,
+    I18N_EXEC_HELP,
+    I18N_EXEC_USERS_USAGE,
+    I18N_EXEC_STATS_USAGE,
+    I18N_EXEC_TAIL_USAGE,
+    I18N_EXEC_POST_USAGE,
+    I18N_EXEC_POST_EMPTY,
+    I18N_EXEC_POST_INVALID_UTF8,
+    I18N_EXEC_UNKNOWN_COMMAND_FORMAT,
     I18N_CONTINUE_PROMPT
 } i18n_text_id_t;
 
diff --git a/src/exec.c b/src/exec.c
index 37dfd37..319d661 100644
--- a/src/exec.c
+++ b/src/exec.c
@@ -2,6 +2,7 @@
 #include "chat_room.h"
 #include "client.h"
 #include "common.h"
+#include "i18n.h"
 #include "input.h"
 #include "message.h"
 #include "ratelimit.h"
@@ -116,21 +117,9 @@ static void resolve_exec_username(const client_t *client, char *buffer,
 }
 
 static int exec_command_help(client_t *client) {
-    static const char help_text[] =
-        "TNT exec interface\n"
-        "Commands:\n"
-        "  help            Show this help\n"
-        "  health          Print service health\n"
-        "  users [--json]  List online users\n"
-        "  stats [--json]  Print room statistics\n"
-        "  tail [N]        Print recent messages\n"
-        "  tail -n N       Print recent messages\n"
-        "  post MESSAGE    Post a message non-interactively\n"
-        "  post \"/me act\"  Post an action message\n"
-        "  support         Show quick support guide\n"
-        "  exit            Exit successfully\n";
+    const char *help_text = i18n_text(client->help_lang, I18N_EXEC_HELP);
 
-    return client_send(client, help_text, sizeof(help_text) - 1) == 0 ? 0 : 1;
+    return client_send(client, help_text, strlen(help_text)) == 0 ? 0 : 1;
 }
 
 static int exec_command_support(client_t *client) {
@@ -304,7 +293,8 @@ static int exec_command_tail(client_t *client, const char *args) {
     int rc;
 
     if (parse_tail_count(args, &requested) < 0) {
-        client_printf(client, "tail: usage: tail [N] | tail -n N\n");
+        client_printf(client, "%s",
+                      i18n_text(client->help_lang, I18N_EXEC_TAIL_USAGE));
         return 64;
     }
 
@@ -357,7 +347,8 @@ static int exec_command_post(client_t *client, const char *args) {
     };
 
     if (!args || args[0] == '\0') {
-        client_printf(client, "post: usage: post MESSAGE\n");
+        client_printf(client, "%s",
+                      i18n_text(client->help_lang, I18N_EXEC_POST_USAGE));
         return 64;
     }
 
@@ -366,12 +357,15 @@ static int exec_command_post(client_t *client, const char *args) {
     trim_ascii_whitespace(content);
 
     if (content[0] == '\0') {
-        client_printf(client, "post: message cannot be empty\n");
+        client_printf(client, "%s",
+                      i18n_text(client->help_lang, I18N_EXEC_POST_EMPTY));
         return 64;
     }
 
     if (!utf8_is_valid_string(content)) {
-        client_printf(client, "post: invalid UTF-8 input\n");
+        client_printf(client, "%s",
+                      i18n_text(client->help_lang,
+                                I18N_EXEC_POST_INVALID_UTF8));
         return 1;
     }
 
@@ -443,14 +437,18 @@ int exec_dispatch(client_t *client) {
     }
     if (strcmp(cmd, "users") == 0) {
         if (args && strcmp(args, "--json") != 0) {
-            client_printf(client, "users: usage: users [--json]\n");
+            client_printf(client, "%s",
+                          i18n_text(client->help_lang,
+                                    I18N_EXEC_USERS_USAGE));
             return 64;
         }
         return exec_command_users(client, args != NULL);
     }
     if (strcmp(cmd, "stats") == 0) {
         if (args && strcmp(args, "--json") != 0) {
-            client_printf(client, "stats: usage: stats [--json]\n");
+            client_printf(client, "%s",
+                          i18n_text(client->help_lang,
+                                    I18N_EXEC_STATS_USAGE));
             return 64;
         }
         return exec_command_stats(client, args != NULL);
@@ -465,6 +463,9 @@ int exec_dispatch(client_t *client) {
         return 0;
     }
 
-    client_printf(client, "Unknown command: %s\n", cmd);
+    client_printf(client,
+                  i18n_text(client->help_lang,
+                            I18N_EXEC_UNKNOWN_COMMAND_FORMAT),
+                  cmd);
     return 64;
 }
diff --git a/src/i18n.c b/src/i18n.c
index d29bc02..90a333c 100644
--- a/src/i18n.c
+++ b/src/i18n.c
@@ -168,6 +168,33 @@ const char *i18n_text(help_lang_t lang, i18n_text_id_t id) {
                 return "你是想输入 :%s 吗?\n";
             case I18N_UNKNOWN_GUIDANCE:
                 return "输入 :support 查看引导，或 :help 查看命令\n";
+            case I18N_EXEC_HELP:
+                return "TNT exec 接口\n"
+                       "命令:\n"
+                       "  help            显示此帮助\n"
+                       "  health          输出服务健康状态\n"
+                       "  users [--json]  列出在线用户\n"
+                       "  stats [--json]  输出房间统计\n"
+                       "  tail [N]        输出最近消息\n"
+                       "  tail -n N       输出最近消息\n"
+                       "  post MESSAGE    非交互发送消息\n"
+                       "  post \"/me act\" 发送动作消息\n"
+                       "  support         显示快速支持指南\n"
+                       "  exit            成功退出\n";
+            case I18N_EXEC_USERS_USAGE:
+                return "users: 用法: users [--json]\n";
+            case I18N_EXEC_STATS_USAGE:
+                return "stats: 用法: stats [--json]\n";
+            case I18N_EXEC_TAIL_USAGE:
+                return "tail: 用法: tail [N] | tail -n N\n";
+            case I18N_EXEC_POST_USAGE:
+                return "post: 用法: post MESSAGE\n";
+            case I18N_EXEC_POST_EMPTY:
+                return "post: 消息不能为空\n";
+            case I18N_EXEC_POST_INVALID_UTF8:
+                return "post: 输入不是有效 UTF-8\n";
+            case I18N_EXEC_UNKNOWN_COMMAND_FORMAT:
+                return "未知命令: %s\n";
             case I18N_CONTINUE_PROMPT:
                 return "\n按任意键继续...";
         }
@@ -271,6 +298,33 @@ const char *i18n_text(help_lang_t lang, i18n_text_id_t id) {
             return "Did you mean :%s?\n";
         case I18N_UNKNOWN_GUIDANCE:
             return "Type :support for guidance or :help for commands\n";
+        case I18N_EXEC_HELP:
+            return "TNT exec interface\n"
+                   "Commands:\n"
+                   "  help            Show this help\n"
+                   "  health          Print service health\n"
+                   "  users [--json]  List online users\n"
+                   "  stats [--json]  Print room statistics\n"
+                   "  tail [N]        Print recent messages\n"
+                   "  tail -n N       Print recent messages\n"
+                   "  post MESSAGE    Post a message non-interactively\n"
+                   "  post \"/me act\"  Post an action message\n"
+                   "  support         Show quick support guide\n"
+                   "  exit            Exit successfully\n";
+        case I18N_EXEC_USERS_USAGE:
+            return "users: usage: users [--json]\n";
+        case I18N_EXEC_STATS_USAGE:
+            return "stats: usage: stats [--json]\n";
+        case I18N_EXEC_TAIL_USAGE:
+            return "tail: usage: tail [N] | tail -n N\n";
+        case I18N_EXEC_POST_USAGE:
+            return "post: usage: post MESSAGE\n";
+        case I18N_EXEC_POST_EMPTY:
+            return "post: message cannot be empty\n";
+        case I18N_EXEC_POST_INVALID_UTF8:
+            return "post: invalid UTF-8 input\n";
+        case I18N_EXEC_UNKNOWN_COMMAND_FORMAT:
+            return "Unknown command: %s\n";
         case I18N_CONTINUE_PROMPT:
             return "\nPress any key to continue...";
     }
diff --git a/tests/test_exec_mode.sh b/tests/test_exec_mode.sh
index 3974dff..880f22d 100755
--- a/tests/test_exec_mode.sh
+++ b/tests/test_exec_mode.sh
@@ -87,6 +87,40 @@ else
     FAIL=$((FAIL + 1))
 fi
 
+HELP_OUTPUT=$(ssh $SSH_OPTS localhost help 2>/dev/null || true)
+printf '%s\n' "$HELP_OUTPUT" | grep -q '^TNT exec 接口$' &&
+printf '%s\n' "$HELP_OUTPUT" | grep -q '^命令:$'
+if [ $? -eq 0 ]; then
+    echo "✓ help follows TNT_LANG"
+    PASS=$((PASS + 1))
+else
+    echo "✗ help output unexpected"
+    printf '%s\n' "$HELP_OUTPUT"
+    FAIL=$((FAIL + 1))
+fi
+
+UNKNOWN_OUTPUT=$(ssh $SSH_OPTS localhost nope 2>/dev/null || true)
+printf '%s\n' "$UNKNOWN_OUTPUT" | grep -q '^未知命令: nope$'
+if [ $? -eq 0 ]; then
+    echo "✓ unknown command follows TNT_LANG"
+    PASS=$((PASS + 1))
+else
+    echo "✗ unknown command output unexpected"
+    printf '%s\n' "$UNKNOWN_OUTPUT"
+    FAIL=$((FAIL + 1))
+fi
+
+POST_USAGE=$(ssh $SSH_OPTS localhost post 2>/dev/null || true)
+printf '%s\n' "$POST_USAGE" | grep -q '^post: 用法: post MESSAGE$'
+if [ $? -eq 0 ]; then
+    echo "✓ post usage follows TNT_LANG"
+    PASS=$((PASS + 1))
+else
+    echo "✗ post usage output unexpected"
+    printf '%s\n' "$POST_USAGE"
+    FAIL=$((FAIL + 1))
+fi
+
 POST_OUTPUT=$(ssh $SSH_OPTS execposter@localhost post "hello from exec" 2>/dev/null || true)
 if [ "$POST_OUTPUT" = "posted" ]; then
     echo "✓ post publishes a message"
diff --git a/tests/unit/test_i18n.c b/tests/unit/test_i18n.c
index 4dc4780..ea587f6 100644
--- a/tests/unit/test_i18n.c
+++ b/tests/unit/test_i18n.c
@@ -98,6 +98,18 @@ TEST(text_lookup_matches_language) {
                   "Unknown command") != NULL);
     assert(strstr(i18n_text(LANG_ZH, I18N_UNKNOWN_COMMAND_FORMAT),
                   "未知命令") != NULL);
+    assert(strstr(i18n_text(LANG_EN, I18N_EXEC_HELP),
+                  "TNT exec interface") != NULL);
+    assert(strstr(i18n_text(LANG_ZH, I18N_EXEC_HELP),
+                  "TNT exec 接口") != NULL);
+    assert(strstr(i18n_text(LANG_EN, I18N_EXEC_POST_EMPTY),
+                  "message cannot be empty") != NULL);
+    assert(strstr(i18n_text(LANG_ZH, I18N_EXEC_POST_EMPTY),
+                  "消息不能为空") != NULL);
+    assert(strstr(i18n_text(LANG_EN, I18N_EXEC_UNKNOWN_COMMAND_FORMAT),
+                  "Unknown command") != NULL);
+    assert(strstr(i18n_text(LANG_ZH, I18N_EXEC_UNKNOWN_COMMAND_FORMAT),
+                  "未知命令") != NULL);
     assert(strcmp(i18n_lang_code(LANG_EN), "en") == 0);
     assert(strcmp(i18n_lang_code(LANG_ZH), "zh") == 0);
 }