diff --git a/application/src/main/java/run/halo/app/infra/webfilter/LocaleChangeWebFilter.java b/application/src/main/java/run/halo/app/infra/webfilter/LocaleChangeWebFilter.java
index 3233d4ad5..9f25e98b0 100644
--- a/application/src/main/java/run/halo/app/infra/webfilter/LocaleChangeWebFilter.java
+++ b/application/src/main/java/run/halo/app/infra/webfilter/LocaleChangeWebFilter.java
@@ -3,6 +3,7 @@ package run.halo.app.infra.webfilter;
 import static run.halo.app.theme.ThemeLocaleContextResolver.LANGUAGE_COOKIE_NAME;
 
 import java.util.Locale;
+import java.util.Objects;
 import java.util.Set;
 import org.springframework.core.Ordered;
 import org.springframework.core.annotation.Order;
@@ -45,20 +46,24 @@ public class LocaleChangeWebFilter implements WebFilter {
     @Override
     @NonNull
     public Mono<Void> filter(ServerWebExchange exchange, @NonNull WebFilterChain chain) {
-        var request = exchange.getRequest();
         return matcher.matches(exchange)
             .filter(MatchResult::isMatch)
             .doOnNext(result -> {
                 var localeContext = themeLocaleContextResolver.resolveLocaleContext(exchange);
                 var locale = localeContext.getLocale();
                 if (locale != null) {
-                    setLanguageCookie(exchange, locale);
+                    setLanguageCookieIfAbsent(exchange, locale);
                 }
             })
             .then(Mono.defer(() -> chain.filter(exchange)));
     }
 
-    void setLanguageCookie(ServerWebExchange exchange, Locale locale) {
+    void setLanguageCookieIfAbsent(ServerWebExchange exchange, Locale locale) {
+        var languageCookie = exchange.getRequest().getCookies().getFirst(LANGUAGE_COOKIE_NAME);
+        if (languageCookie != null
+            && Objects.equals(languageCookie.getValue(), locale.toLanguageTag())) {
+            return;
+        }
         var cookie = ResponseCookie.from(LANGUAGE_COOKIE_NAME, locale.toLanguageTag())
             .path("/")
             .secure("https".equalsIgnoreCase(exchange.getRequest().getURI().getScheme()))
diff --git a/application/src/main/java/run/halo/app/theme/ThemeLocaleContextResolver.java b/application/src/main/java/run/halo/app/theme/ThemeLocaleContextResolver.java
index 3d23b2f64..da6b608a0 100644
--- a/application/src/main/java/run/halo/app/theme/ThemeLocaleContextResolver.java
+++ b/application/src/main/java/run/halo/app/theme/ThemeLocaleContextResolver.java
@@ -4,6 +4,7 @@ import java.util.Locale;
 import java.util.Optional;
 import java.util.TimeZone;
 import lombok.extern.slf4j.Slf4j;
+import org.apache.commons.lang3.LocaleUtils;
 import org.apache.commons.lang3.StringUtils;
 import org.springframework.context.i18n.LocaleContext;
 import org.springframework.context.i18n.SimpleTimeZoneAwareLocaleContext;
@@ -39,6 +40,10 @@ public class ThemeLocaleContextResolver extends AcceptHeaderLocaleContextResolve
             .or(() -> UserLocaleRequestAttributeWriteFilter.getUserLocale(request))
             .orElseGet(() -> super.resolveLocaleContext(exchange).getLocale());
 
+        if (LocaleUtils.isLanguageUndetermined(locale)) {
+            locale = null;
+        }
+
         var timeZone = getTimeZoneFromCookie(request)
             .orElseGet(TimeZone::getDefault);
 
diff --git a/application/src/test/java/run/halo/app/theme/ThemeLocaleContextResolverTest.java b/application/src/test/java/run/halo/app/theme/ThemeLocaleContextResolverTest.java
index a1ada782e..2e5cc3985 100644
--- a/application/src/test/java/run/halo/app/theme/ThemeLocaleContextResolverTest.java
+++ b/application/src/test/java/run/halo/app/theme/ThemeLocaleContextResolverTest.java
@@ -177,6 +177,15 @@ class ThemeLocaleContextResolverTest {
         assertThat(this.resolver.resolveLocaleContext(exchange).getLocale()).isEqualTo(US);
     }
 
+    @Test
+    void resolveUnderminedLocale() {
+        var request = MockServerHttpRequest.get("/")
+            .header(HttpHeaders.ACCEPT_LANGUAGE, "und")
+            .build();
+        var exchange = MockServerWebExchange.from(request);
+
+        assertThat(this.resolver.resolveLocaleContext(exchange).getLocale()).isNull();
+    }
 
     private ServerWebExchange exchange(Locale... locales) {
         return MockServerWebExchange.from(
diff --git a/application/src/test/java/run/halo/app/webfilter/LocaleChangeWebFilterTest.java b/application/src/test/java/run/halo/app/webfilter/LocaleChangeWebFilterTest.java
index 4d336bc4a..f11db04da 100644
--- a/application/src/test/java/run/halo/app/webfilter/LocaleChangeWebFilterTest.java
+++ b/application/src/test/java/run/halo/app/webfilter/LocaleChangeWebFilterTest.java
@@ -9,6 +9,7 @@ import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
+import org.springframework.http.HttpCookie;
 import org.springframework.http.MediaType;
 import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
 import org.springframework.mock.web.server.MockServerWebExchange;
@@ -44,11 +45,43 @@ class LocaleChangeWebFilterTest {
     }
 
     @Test
-    void shouldRespondLanguageCookieWithUndefinedLanguageTag() {
+    void shouldNotRespondLanguageCookieIfChanged() {
         WebFilterChain webFilterChain = filterExchange -> {
             var languageCookie = filterExchange.getResponse().getCookies().getFirst("language");
             assertNotNull(languageCookie);
-            assertEquals("und", languageCookie.getValue());
+            assertEquals("zh-CN", languageCookie.getValue());
+            return Mono.empty();
+        };
+        var exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/home")
+            .accept(MediaType.TEXT_HTML)
+            .cookie(new HttpCookie("language", "zh-HK"))
+            .queryParam("language", "zh-CN")
+            .build()
+        );
+        this.filter.filter(exchange, webFilterChain).block();
+    }
+
+    @Test
+    void shouldNotRespondLanguageCookieIfNotChanged() {
+        WebFilterChain webFilterChain = filterExchange -> {
+            var languageCookie = filterExchange.getResponse().getCookies().getFirst("language");
+            assertNull(languageCookie);
+            return Mono.empty();
+        };
+        var exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/home")
+            .accept(MediaType.TEXT_HTML)
+            .cookie(new HttpCookie("language", "zh-CN"))
+            .queryParam("language", "zh-CN")
+            .build()
+        );
+        this.filter.filter(exchange, webFilterChain).block();
+    }
+
+    @Test
+    void shouldNotRespondLanguageCookieWithUndeterminedLanguageTag() {
+        WebFilterChain webFilterChain = filterExchange -> {
+            var languageCookie = filterExchange.getResponse().getCookies().getFirst("language");
+            assertNull(languageCookie);
             return Mono.empty();
         };
         var exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/home")