diff --git a/src/scripts/core/root.js b/src/scripts/core/root.js
index 686aa90..2445393 100644
--- a/src/scripts/core/root.js
+++ b/src/scripts/core/root.js
@@ -40,7 +40,8 @@
 
             var matchPreferColorScheme = $window.matchMedia('(prefers-color-scheme: dark)');
 
-            ariaNgLogService.info(matchPreferColorScheme)
+            ariaNgLogService.info('[root.setThemeBySystemSettings] system uses ' + (matchPreferColorScheme.matches ? 'dark' : 'light') + ' theme');
+
             if (matchPreferColorScheme.matches) {
                 setDarkTheme();
             } else {
@@ -453,6 +454,8 @@
         if (ariaNgSettingService.isBrowserSupportMatchMedia()) {
             var matchPreferColorScheme = $window.matchMedia('(prefers-color-scheme: dark)');
             matchPreferColorScheme.addEventListener('change', function (e) {
+                ariaNgLogService.info('[root] system switches to ' + (e.matches ? 'dark' : 'light') + ' theme');
+
                 if (ariaNgSettingService.getTheme() === 'system') {
                     if (e.matches) {
                         setDarkTheme();
diff --git a/src/scripts/services/ariaNgSettingService.js b/src/scripts/services/ariaNgSettingService.js
index d11bc89..b42629c 100644
--- a/src/scripts/services/ariaNgSettingService.js
+++ b/src/scripts/services/ariaNgSettingService.js
@@ -86,6 +86,7 @@
             var browserLang = $window.navigator.browserLanguage ? $window.navigator.browserLanguage : $window.navigator.language;
 
             if (!browserLang) {
+                ariaNgLogService.info('[ariaNgSettingService] cannot get browser language, use default language');
                 return ariaNgDefaultOptions.language;
             }
 
@@ -113,9 +114,11 @@
             }
 
             if (!ariaNgLanguages[browserLang]) {
+                ariaNgLogService.info('[ariaNgSettingService] browser language \"' + browserLang + '\" not support, use default language');
                 return ariaNgDefaultOptions.language;
             }
 
+            ariaNgLogService.info('[ariaNgSettingService] use browser language \"' + browserLang + '\" as current language');
             return browserLang;
         };