getDetail에 languageCode를 optional로 변경하여 languageCode가 없어도 정상 조회 되도록 수정

src/main/kotlin/kr/co/vividnext/sodalive/content/AudioContentController.kt

@@ -131,7 +131,7 @@ class AudioContentController(private val service: AudioContentService) {
     fun getDetail(
         @PathVariable id: Long,
         @RequestParam timezone: String,
-        @RequestParam(required = false, defaultValue = "ko") languageCode: String? = "ko",
+        @RequestParam(required = false) languageCode: String? = null,
         @RequestParam("isAdultContentVisible", required = false) isAdultContentVisible: Boolean? = null,
         @AuthenticationPrincipal(expression = "#this == 'anonymousUser' ? null : member") member: Member?
     ) = run {
@@ -143,7 +143,7 @@ class AudioContentController(private val service: AudioContentService) {
                 member = member,
                 isAdultContentVisible = isAdultContentVisible ?: true,
                 timezone = timezone,
-                languageCode = languageCode ?: "ko"
+                languageCode = languageCode
             )
         )
     }