diff --git a/resources/lang/pt_BR.json b/resources/lang/pt-BR.json
similarity index 99%
rename from resources/lang/pt_BR.json
rename to resources/lang/pt-BR.json
index f058409fc..c615438e6 100644
--- a/resources/lang/pt_BR.json
+++ b/resources/lang/pt-BR.json
@@ -167,7 +167,7 @@
     "en": "Brazilian Portuguese",
     "native": "Português brasileiro",
     "svg": "br",
-    "lang_code": "pt_BR"
+    "lang_code": "pt-BR"
   },
   "game_mode": {
     "ffa": "Free for All",
diff --git a/resources/lang/sv_SE.json b/resources/lang/sv-SE.json
similarity index 99%
rename from resources/lang/sv_SE.json
rename to resources/lang/sv-SE.json
index 4415ccc85..0c50034c5 100644
--- a/resources/lang/sv_SE.json
+++ b/resources/lang/sv-SE.json
@@ -3,7 +3,7 @@
     "en": "Swedish",
     "native": "Svenska",
     "svg": "se",
-    "lang_code": "sv_SE"
+    "lang_code": "sv-SE"
   },
   "common": {
     "close": "Stäng"
diff --git a/resources/lang/zh_CN.json b/resources/lang/zh-CN.json
similarity index 99%
rename from resources/lang/zh_CN.json
rename to resources/lang/zh-CN.json
index 700a910e9..becaf5649 100644
--- a/resources/lang/zh_CN.json
+++ b/resources/lang/zh-CN.json
@@ -3,7 +3,7 @@
     "en": "Chinese Simplified",
     "native": "简体中文",
     "svg": "cn",
-    "lang_code": "zh_CN"
+    "lang_code": "zh-CN"
   },
   "common": {
     "close": "关闭"
diff --git a/src/client/LangSelector.ts b/src/client/LangSelector.ts
index 783ecdced..d65f3c4d1 100644
--- a/src/client/LangSelector.ts
+++ b/src/client/LangSelector.ts
@@ -21,14 +21,14 @@ import ja from "../../resources/lang/ja.json";
 import ko from "../../resources/lang/ko.json";
 import nl from "../../resources/lang/nl.json";
 import pl from "../../resources/lang/pl.json";
-import pt_BR from "../../resources/lang/pt_BR.json";
+import pt_BR from "../../resources/lang/pt-BR.json";
 import ru from "../../resources/lang/ru.json";
 import sh from "../../resources/lang/sh.json";
-import sv_SE from "../../resources/lang/sv_SE.json";
+import sv_SE from "../../resources/lang/sv-SE.json";
 import tp from "../../resources/lang/tp.json";
 import tr from "../../resources/lang/tr.json";
 import uk from "../../resources/lang/uk.json";
-import zh_CN from "../../resources/lang/zh_CN.json";
+import zh_CN from "../../resources/lang/zh-CN.json";
 
 @customElement("lang-selector")
 export class LangSelector extends LitElement {
@@ -55,7 +55,7 @@ export class LangSelector extends LitElement {
     ja,
     nl,
     pl,
-    pt_BR,
+    "pt-BR": pt_BR,
     ru,
     sh,
     tr,
@@ -65,8 +65,8 @@ export class LangSelector extends LitElement {
     he,
     da,
     fi,
-    sv_SE,
-    zh_CN,
+    "sv-SE": sv_SE,
+    "zh-CN": zh_CN,
     ko,
     gl,
   };
@@ -93,8 +93,16 @@ export class LangSelector extends LitElement {
   private getClosestSupportedLang(lang: string): string {
     if (!lang) return "en";
     if (lang in this.languageMap) return lang;
-    const base = lang.split("-")[0];
-    if (base in this.languageMap) return base;
+
+    const base = lang.slice(0, 2);
+    const candidates = Object.keys(this.languageMap).filter((key) =>
+      key.startsWith(base),
+    );
+    if (candidates.length > 0) {
+      candidates.sort((a, b) => b.length - a.length); // More specific first
+      return candidates[0];
+    }
+
     return "en";
   }