diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 4a139da..0a3204b 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -46,6 +46,8 @@
 - Language selection is limited to stable codes (`en`, `zh`) and
   locale-shaped environment values; natural-language labels are not accepted
   as command arguments.
+- Full-screen help now uses `l` to cycle the UI language through the i18n
+  module instead of hard-coding one key per language.
 - Documented i18n and user-facing text rules for English-first source text,
   stable command syntax, concise help copy, and translation-only localization.
 
diff --git a/include/i18n.h b/include/i18n.h
index b6c105b..986f99f 100644
--- a/include/i18n.h
+++ b/include/i18n.h
@@ -58,6 +58,7 @@ typedef enum {
 bool i18n_try_parse_ui_lang(const char *value, ui_lang_t *lang);
 ui_lang_t i18n_parse_ui_lang(const char *value, ui_lang_t fallback);
 ui_lang_t i18n_default_ui_lang(void);
+ui_lang_t i18n_next_ui_lang(ui_lang_t lang);
 const char *i18n_ui_lang_code(ui_lang_t lang);
 const char *i18n_text(ui_lang_t lang, i18n_text_id_t id);
 
diff --git a/src/help_text.c b/src/help_text.c
index 13ec3e1..797f1ae 100644
--- a/src/help_text.c
+++ b/src/help_text.c
@@ -56,7 +56,7 @@ void help_text_append_full(char *buffer, size_t buf_size, size_t *pos,
                        "  Ctrl+D/U   - Scroll half page down/up\n"
                        "  Ctrl+F/B   - Scroll full page down/up\n"
                        "  g/G        - Jump to top/bottom\n"
-                       "  e/z        - Switch English/Chinese\n");
+                       "  l          - Cycle UI language\n");
         return;
     }
 
@@ -111,5 +111,5 @@ void help_text_append_full(char *buffer, size_t buf_size, size_t *pos,
                    "  Ctrl+D/U   - 向下/上滚动半页\n"
                    "  Ctrl+F/B   - 向下/上滚动整页\n"
                    "  g/G        - 跳到顶部/底部\n"
-                   "  e/z        - 切换英文/中文\n");
+                   "  l          - 切换界面语言\n");
 }
diff --git a/src/i18n.c b/src/i18n.c
index 38b3a3d..2999be8 100644
--- a/src/i18n.c
+++ b/src/i18n.c
@@ -81,6 +81,10 @@ ui_lang_t i18n_default_ui_lang(void) {
     return i18n_parse_ui_lang(locale, UI_LANG_EN);
 }
 
+ui_lang_t i18n_next_ui_lang(ui_lang_t lang) {
+    return lang == UI_LANG_EN ? UI_LANG_ZH : UI_LANG_EN;
+}
+
 const char *i18n_ui_lang_code(ui_lang_t lang) {
     return lang == UI_LANG_ZH ? "zh" : "en";
 }
diff --git a/src/i18n_text.c b/src/i18n_text.c
index 8568163..cfe5368 100644
--- a/src/i18n_text.c
+++ b/src/i18n_text.c
@@ -51,8 +51,8 @@ static const i18n_text_entry_t text_catalog[I18N_TEXT_COUNT] = {
         " 按键 "
     },
     [I18N_HELP_STATUS_FORMAT] = {
-        "-- KEY REFERENCE -- (%d/%d) j/k:scroll g/G:top/bottom e/z:lang q:close",
-        "-- 按键参考 -- (%d/%d) j/k:滚动 g/G:首尾 e/z:语言 q:关闭"
+        "-- KEY REFERENCE -- (%d/%d) j/k:scroll g/G:top/bottom l:lang q:close",
+        "-- 按键参考 -- (%d/%d) j/k:滚动 g/G:首尾 l:语言 q:关闭"
     },
     [I18N_COMMAND_OUTPUT_TITLE] = {
         " COMMAND OUTPUT ",
diff --git a/src/input.c b/src/input.c
index 6172a5f..9468053 100644
--- a/src/input.c
+++ b/src/input.c
@@ -257,12 +257,8 @@ static bool handle_key(client_t *client, unsigned char key, char *input) {
         if (key == 'q' || key == 27) {
             client->show_help = false;
             tui_render_screen(client);
-        } else if (key == 'e' || key == 'E') {
-            client->ui_lang = UI_LANG_EN;
-            client->help_scroll_pos = 0;
-            tui_render_help(client);
-        } else if (key == 'z' || key == 'Z') {
-            client->ui_lang = UI_LANG_ZH;
+        } else if (key == 'l' || key == 'L') {
+            client->ui_lang = i18n_next_ui_lang(client->ui_lang);
             client->help_scroll_pos = 0;
             tui_render_help(client);
         } else if (key == 'j') {
diff --git a/tests/test_interactive_input.sh b/tests/test_interactive_input.sh
index 54aa175..cc457e4 100755
--- a/tests/test_interactive_input.sh
+++ b/tests/test_interactive_input.sh
@@ -149,6 +149,14 @@ expect "TNT\\(1\\) 帮助"
 expect "q:关闭"
 send -- "q"
 expect "NORMAL"
+send -- "?"
+expect "TNT 按键参考"
+expect "l:语言"
+send -- "l"
+expect "TNT KEY REFERENCE"
+expect "l:lang"
+send -- "q"
+expect "NORMAL"
 send -- ":"
 expect ":"
 send -- "lang en\r"
diff --git a/tests/unit/test_help_text.c b/tests/unit/test_help_text.c
index 7589746..acb4129 100644
--- a/tests/unit/test_help_text.c
+++ b/tests/unit/test_help_text.c
@@ -31,7 +31,8 @@ TEST(full_help_matches_language) {
     assert(strstr(en, ":inbox") != NULL);
     assert(strstr(en, ":support") == NULL);
     assert(strstr(en, ":commands") == NULL);
-    assert(strstr(en, "Switch English/Chinese") != NULL);
+    assert(strstr(en, "Cycle UI language") != NULL);
+    assert(strstr(en, "Switch English/Chinese") == NULL);
 
     assert(strstr(zh, "TNT 按键参考") != NULL);
     assert(strstr(zh, "可用命令") != NULL);
@@ -43,7 +44,8 @@ TEST(full_help_matches_language) {
     assert(strstr(zh, "@用户名") == NULL);
     assert(strstr(zh, ":support") == NULL);
     assert(strstr(zh, ":commands") == NULL);
-    assert(strstr(zh, "切换英文/中文") != NULL);
+    assert(strstr(zh, "切换界面语言") != NULL);
+    assert(strstr(zh, "切换英文/中文") == NULL);
     assert_ascii_angle_placeholders(zh);
 }
 
diff --git a/tests/unit/test_i18n.c b/tests/unit/test_i18n.c
index 5cd4e78..fa7baef 100644
--- a/tests/unit/test_i18n.c
+++ b/tests/unit/test_i18n.c
@@ -89,8 +89,12 @@ TEST(text_lookup_matches_language) {
                   "匿名聊天室") != NULL);
     assert(strstr(i18n_text(UI_LANG_EN, I18N_HELP_STATUS_FORMAT),
                   "KEY REFERENCE") != NULL);
+    assert(strstr(i18n_text(UI_LANG_EN, I18N_HELP_STATUS_FORMAT),
+                  "l:lang") != NULL);
     assert(strstr(i18n_text(UI_LANG_ZH, I18N_HELP_STATUS_FORMAT),
                   "按键参考") != NULL);
+    assert(strstr(i18n_text(UI_LANG_ZH, I18N_HELP_STATUS_FORMAT),
+                  "l:语言") != NULL);
     assert(strstr(i18n_text(UI_LANG_EN, I18N_COMMAND_OUTPUT_TITLE),
                   "COMMAND") != NULL);
     assert(strstr(i18n_text(UI_LANG_ZH, I18N_COMMAND_OUTPUT_TITLE),
@@ -141,6 +145,8 @@ TEST(text_lookup_matches_language) {
                   "未知命令") != NULL);
     assert(strcmp(i18n_ui_lang_code(UI_LANG_EN), "en") == 0);
     assert(strcmp(i18n_ui_lang_code(UI_LANG_ZH), "zh") == 0);
+    assert(i18n_next_ui_lang(UI_LANG_EN) == UI_LANG_ZH);
+    assert(i18n_next_ui_lang(UI_LANG_ZH) == UI_LANG_EN);
 }
 
 TEST(text_catalog_is_complete) {