diff --git a/docs/20260402_시리즈배너언어별조회적용.md b/docs/20260402_시리즈배너언어별조회적용.md
new file mode 100644
index 00000000..fe218b3c
--- /dev/null
+++ b/docs/20260402_시리즈배너언어별조회적용.md
@@ -0,0 +1,10 @@
+- [x] 시리즈 배너 등록·조회 경로와 언어 처리 기준을 확인한다.
+- [x] 배너 등록 시 언어를 저장하고 관리자 목록에서 시리즈 제목에 `(언어)` 표기를 추가한다.
+- [x] 사용자 시리즈 메인 조회에서 요청 언어와 일치하는 배너만 반환하도록 수정하고 검증 결과를 기록한다.
+
+## 검증 기록
+
+### 1차 구현
+- 무엇을: 시리즈 배너 등록 요청에 `lang`을 추가하고, 관리자 목록에서는 `seriesTitle (언어)` 형태로 응답하며, 사용자 시리즈 메인에서는 `LangContext`와 일치하는 언어 배너만 조회하도록 수정했다.
+- 왜: 관리자 화면에서는 같은 시리즈명의 다국어 배너를 구분할 수 있어야 하고, 사용자 화면에서는 요청 언어와 맞는 배너만 노출되어야 하기 때문이다.
+- 어떻게: Kotlin LSP가 없어 정적 진단은 Gradle 컴파일로 대체했고, `./gradlew test --tests "kr.co.vividnext.sodalive.content.series.main.banner.ContentSeriesBannerServiceTest" --tests "kr.co.vividnext.sodalive.admin.content.series.banner.AdminContentSeriesBannerControllerTest" --tests "kr.co.vividnext.sodalive.content.series.main.SeriesMainControllerTest"`를 실행해 등록 언어 저장, 관리자 목록 언어 표기, 사용자 언어별 배너 조회를 검증했다. 결과는 `BUILD SUCCESSFUL`이다.
diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/AdminContentSeriesBannerController.kt b/src/main/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/AdminContentSeriesBannerController.kt
index 6f8c3d4b..7ec2edd5 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/AdminContentSeriesBannerController.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/AdminContentSeriesBannerController.kt
@@ -56,7 +56,9 @@ class AdminContentSeriesBannerController(
         val banners = bannerService.getActiveBanners(pageable)
         val response = SeriesBannerListPageResponse(
             totalCount = banners.totalElements,
-            content = banners.content.map { SeriesBannerResponse.from(it, imageHost) }
+            content = banners.content.map {
+                SeriesBannerResponse.from(it, imageHost, appendLanguageToSeriesTitle = true)
+            }
         )
         ApiResponse.ok(response)
     }
@@ -82,7 +84,7 @@ class AdminContentSeriesBannerController(
         val objectMapper = ObjectMapper()
         val request = objectMapper.readValue(requestString, SeriesBannerRegisterRequest::class.java)
 
-        val banner = bannerService.registerBanner(seriesId = request.seriesId, imagePath = "")
+        val banner = bannerService.registerBanner(seriesId = request.seriesId, imagePath = "", lang = request.lang)
         val imagePath = saveImage(banner.id!!, image)
         val updatedBanner = bannerService.updateBanner(banner.id!!, imagePath)
         val response = SeriesBannerResponse.from(updatedBanner, imageHost)
diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/dto/SeriesBannerDtos.kt b/src/main/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/dto/SeriesBannerDtos.kt
index d054ca91..a8537476 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/dto/SeriesBannerDtos.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/dto/SeriesBannerDtos.kt
@@ -2,10 +2,12 @@ package kr.co.vividnext.sodalive.admin.content.series.banner.dto
 
 import com.fasterxml.jackson.annotation.JsonProperty
 import kr.co.vividnext.sodalive.content.series.main.banner.SeriesBanner
+import kr.co.vividnext.sodalive.i18n.Lang
 
 // 시리즈 배너 등록 요청 DTO
 data class SeriesBannerRegisterRequest(
-    @JsonProperty("seriesId") val seriesId: Long
+    @JsonProperty("seriesId") val seriesId: Long,
+    @JsonProperty("lang") val lang: Lang? = null
 )
 
 // 시리즈 배너 수정 요청 DTO
@@ -22,14 +24,30 @@ data class SeriesBannerResponse(
     val seriesTitle: String
 ) {
     companion object {
-        fun from(banner: SeriesBanner, imageHost: String): SeriesBannerResponse {
+        fun from(
+            banner: SeriesBanner,
+            imageHost: String,
+            appendLanguageToSeriesTitle: Boolean = false
+        ): SeriesBannerResponse {
             return SeriesBannerResponse(
                 id = banner.id!!,
                 imagePath = "$imageHost/${banner.imagePath}",
                 seriesId = banner.series.id!!,
-                seriesTitle = banner.series.title
+                seriesTitle = if (appendLanguageToSeriesTitle) {
+                    "${banner.series.title} (${getLanguageLabel(banner.lang)})"
+                } else {
+                    banner.series.title
+                }
             )
         }
+
+        private fun getLanguageLabel(lang: Lang): String {
+            return when (lang) {
+                Lang.KO -> "한국어"
+                Lang.EN -> "영어"
+                Lang.JA -> "일본어"
+            }
+        }
     }
 }
 
diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/SeriesMainController.kt b/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/SeriesMainController.kt
index 41c6fde9..0d21dc79 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/SeriesMainController.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/SeriesMainController.kt
@@ -6,6 +6,7 @@ import kr.co.vividnext.sodalive.common.SodaException
 import kr.co.vividnext.sodalive.content.series.ContentSeriesService
 import kr.co.vividnext.sodalive.content.series.main.banner.ContentSeriesBannerService
 import kr.co.vividnext.sodalive.creator.admin.content.series.SeriesPublishedDaysOfWeek
+import kr.co.vividnext.sodalive.i18n.LangContext
 import kr.co.vividnext.sodalive.member.Member
 import kr.co.vividnext.sodalive.member.contentpreference.MemberContentPreferenceService
 import org.springframework.beans.factory.annotation.Value
@@ -21,6 +22,7 @@ import org.springframework.web.bind.annotation.RestController
 class SeriesMainController(
     private val contentSeriesService: ContentSeriesService,
     private val bannerService: ContentSeriesBannerService,
+    private val langContext: LangContext,
     private val memberContentPreferenceService: MemberContentPreferenceService,
 
     @Value("\${cloud.aws.cloud-front.host}")
@@ -33,7 +35,7 @@ class SeriesMainController(
         if (member == null) throw SodaException(messageKey = "common.error.bad_credentials")
         val preference = resolvePreference(member)
 
-        val banners = bannerService.getActiveBanners(PageRequest.of(0, 10))
+        val banners = bannerService.getDisplayBanners(PageRequest.of(0, 10), langContext.lang)
             .content
             .map {
                 SeriesBannerResponse.from(it, imageHost)
diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/ContentSeriesBannerService.kt b/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/ContentSeriesBannerService.kt
index 8ea977b8..fbce2efa 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/ContentSeriesBannerService.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/ContentSeriesBannerService.kt
@@ -2,6 +2,7 @@ package kr.co.vividnext.sodalive.content.series.main.banner
 
 import kr.co.vividnext.sodalive.admin.content.series.AdminContentSeriesRepository
 import kr.co.vividnext.sodalive.common.SodaException
+import kr.co.vividnext.sodalive.i18n.Lang
 import org.springframework.data.domain.Page
 import org.springframework.data.domain.Pageable
 import org.springframework.stereotype.Service
@@ -16,22 +17,28 @@ class ContentSeriesBannerService(
         return bannerRepository.findByIsActiveTrueOrderBySortOrderAsc(pageable)
     }
 
+    fun getDisplayBanners(pageable: Pageable, lang: Lang): Page<SeriesBanner> {
+        return bannerRepository.findByIsActiveTrueAndLangOrderBySortOrderAsc(lang, pageable)
+    }
+
     fun getBannerById(bannerId: Long): SeriesBanner {
         return bannerRepository.findById(bannerId)
             .orElseThrow { SodaException(messageKey = "series.banner.error.not_found") }
     }
 
     @Transactional
-    fun registerBanner(seriesId: Long, imagePath: String): SeriesBanner {
+    fun registerBanner(seriesId: Long, imagePath: String, lang: Lang? = null): SeriesBanner {
         val series = seriesRepository.findByIdAndActiveTrue(seriesId)
             ?: throw SodaException(messageKey = "series.banner.error.series_not_found")
 
         val finalSortOrder = (bannerRepository.findMaxSortOrder() ?: 0) + 1
+        val finalLang = lang ?: Lang.KO
 
         val banner = SeriesBanner(
             imagePath = imagePath,
             series = series,
-            sortOrder = finalSortOrder
+            sortOrder = finalSortOrder,
+            lang = finalLang
         )
         return bannerRepository.save(banner)
     }
diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/SeriesBanner.kt b/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/SeriesBanner.kt
index 2b4cc810..d460cee3 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/SeriesBanner.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/SeriesBanner.kt
@@ -2,7 +2,11 @@ package kr.co.vividnext.sodalive.content.series.main.banner
 
 import kr.co.vividnext.sodalive.common.BaseEntity
 import kr.co.vividnext.sodalive.creator.admin.content.series.Series
+import kr.co.vividnext.sodalive.i18n.Lang
+import javax.persistence.Column
 import javax.persistence.Entity
+import javax.persistence.EnumType
+import javax.persistence.Enumerated
 import javax.persistence.FetchType
 import javax.persistence.JoinColumn
 import javax.persistence.ManyToOne
@@ -25,6 +29,10 @@ class SeriesBanner(
     // 정렬 순서 (낮을수록 먼저 표시)
     var sortOrder: Int = 0,
 
+    @Column(nullable = false)
+    @Enumerated(EnumType.STRING)
+    var lang: Lang = Lang.KO,
+
     // 활성화 여부 (소프트 삭제용)
     var isActive: Boolean = true
 ) : BaseEntity()
diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/SeriesBannerRepository.kt b/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/SeriesBannerRepository.kt
index c2c2052f..b730bab9 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/SeriesBannerRepository.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/SeriesBannerRepository.kt
@@ -1,5 +1,6 @@
 package kr.co.vividnext.sodalive.content.series.main.banner
 
+import kr.co.vividnext.sodalive.i18n.Lang
 import org.springframework.data.domain.Page
 import org.springframework.data.domain.Pageable
 import org.springframework.data.jpa.repository.JpaRepository
@@ -10,6 +11,8 @@ import org.springframework.stereotype.Repository
 interface SeriesBannerRepository : JpaRepository<SeriesBanner, Long> {
     fun findByIsActiveTrueOrderBySortOrderAsc(pageable: Pageable): Page<SeriesBanner>
 
+    fun findByIsActiveTrueAndLangOrderBySortOrderAsc(lang: Lang, pageable: Pageable): Page<SeriesBanner>
+
     @Query("SELECT MAX(b.sortOrder) FROM SeriesBanner b WHERE b.isActive = true")
     fun findMaxSortOrder(): Int?
 }
diff --git a/src/test/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/AdminContentSeriesBannerControllerTest.kt b/src/test/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/AdminContentSeriesBannerControllerTest.kt
new file mode 100644
index 00000000..dc46b303
--- /dev/null
+++ b/src/test/kotlin/kr/co/vividnext/sodalive/admin/content/series/banner/AdminContentSeriesBannerControllerTest.kt
@@ -0,0 +1,108 @@
+package kr.co.vividnext.sodalive.admin.content.series.banner
+
+import com.amazonaws.services.s3.AmazonS3Client
+import com.fasterxml.jackson.databind.ObjectMapper
+import kr.co.vividnext.sodalive.aws.s3.S3Uploader
+import kr.co.vividnext.sodalive.content.series.main.banner.ContentSeriesBannerService
+import kr.co.vividnext.sodalive.content.series.main.banner.SeriesBanner
+import kr.co.vividnext.sodalive.creator.admin.content.series.Series
+import kr.co.vividnext.sodalive.i18n.Lang
+import kr.co.vividnext.sodalive.i18n.LangContext
+import kr.co.vividnext.sodalive.i18n.SodaMessageSource
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+import org.mockito.Mockito
+import org.springframework.data.domain.PageImpl
+import org.springframework.data.domain.PageRequest
+import org.springframework.mock.web.MockMultipartFile
+import java.net.URL
+
+class AdminContentSeriesBannerControllerTest {
+    private val bannerService = Mockito.mock(ContentSeriesBannerService::class.java)
+    private val amazonS3Client = Mockito.mock(AmazonS3Client::class.java)
+    private val s3Uploader = S3Uploader(amazonS3Client)
+    private val controller = AdminContentSeriesBannerController(
+        bannerService = bannerService,
+        s3Uploader = s3Uploader,
+        langContext = LangContext(),
+        messageSource = SodaMessageSource(),
+        s3Bucket = "test-bucket",
+        imageHost = "https://cdn.test"
+    )
+
+    @Test
+    fun shouldRegisterJapaneseBannerThroughAdminApi() {
+        val image = MockMultipartFile("image", "banner.png", "image/png", "image".toByteArray())
+        val registeredBanner = createBanner(id = 10L, lang = Lang.JA, imagePath = "")
+        val updatedBanner = createBanner(id = 10L, lang = Lang.JA, imagePath = "")
+
+        Mockito.`when`(amazonS3Client.getUrl(Mockito.eq("test-bucket"), Mockito.anyString()))
+            .thenAnswer { URL("https://cdn.test/${it.arguments[1]}") }
+
+        Mockito.`when`(
+            bannerService.registerBanner(
+                seriesId = 1L,
+                imagePath = "",
+                lang = Lang.JA
+            )
+        ).thenReturn(registeredBanner)
+        Mockito.doAnswer {
+            updatedBanner.apply {
+                imagePath = it.arguments[1] as String
+            }
+        }.`when`(bannerService).updateBanner(Mockito.eq(10L), Mockito.anyString(), Mockito.isNull())
+
+        val response = controller.registerBanner(
+            image = image,
+            requestString = "{\"seriesId\":1,\"lang\":\"ja\"}"
+        )
+
+        assertTrue(response.success)
+        assertEquals(10L, response.data?.id)
+        assertTrue(response.data?.imagePath?.startsWith("https://cdn.test/series_banner/10/") == true)
+        Mockito.verify(bannerService).registerBanner(1L, "", Lang.JA)
+    }
+
+    @Test
+    fun shouldDeserializeIso639LanguageCodeToLangEnum() {
+        val request = ObjectMapper().readValue(
+            "{\"seriesId\":1,\"lang\":\"en\"}",
+            kr.co.vividnext.sodalive.admin.content.series.banner.dto.SeriesBannerRegisterRequest::class.java
+        )
+
+        assertEquals(Lang.EN, request.lang)
+    }
+
+    @Test
+    fun shouldAppendBannerLanguageToSeriesTitleInBannerList() {
+        val pageable = PageRequest.of(0, 20)
+        val japaneseBanner = createBanner(id = 12L, lang = Lang.JA, imagePath = "banner/jp.png")
+
+        Mockito.`when`(bannerService.getActiveBanners(pageable))
+            .thenReturn(PageImpl(listOf(japaneseBanner), pageable, 1))
+
+        val response = controller.getBannerList(page = 0, size = 20)
+
+        assertTrue(response.success)
+        assertEquals("series-12 (일본어)", response.data?.content?.first()?.seriesTitle)
+    }
+
+    private fun createBanner(id: Long, lang: Lang, imagePath: String): SeriesBanner {
+        val series = Series(
+            title = "series-$id",
+            introduction = "introduction-$id",
+            languageCode = "ko"
+        )
+        series.id = id
+
+        return SeriesBanner(
+            imagePath = imagePath,
+            series = series,
+            sortOrder = 1,
+            lang = lang
+        ).also {
+            it.id = id
+        }
+    }
+}
diff --git a/src/test/kotlin/kr/co/vividnext/sodalive/content/series/main/SeriesMainControllerTest.kt b/src/test/kotlin/kr/co/vividnext/sodalive/content/series/main/SeriesMainControllerTest.kt
new file mode 100644
index 00000000..a560232b
--- /dev/null
+++ b/src/test/kotlin/kr/co/vividnext/sodalive/content/series/main/SeriesMainControllerTest.kt
@@ -0,0 +1,105 @@
+package kr.co.vividnext.sodalive.content.series.main
+
+import kr.co.vividnext.sodalive.content.ContentType
+import kr.co.vividnext.sodalive.content.series.ContentSeriesService
+import kr.co.vividnext.sodalive.content.series.GetSeriesListResponse
+import kr.co.vividnext.sodalive.content.series.main.banner.ContentSeriesBannerService
+import kr.co.vividnext.sodalive.content.series.main.banner.SeriesBanner
+import kr.co.vividnext.sodalive.creator.admin.content.series.Series
+import kr.co.vividnext.sodalive.i18n.Lang
+import kr.co.vividnext.sodalive.i18n.LangContext
+import kr.co.vividnext.sodalive.member.Member
+import kr.co.vividnext.sodalive.member.contentpreference.MemberContentPreferenceService
+import kr.co.vividnext.sodalive.member.contentpreference.ViewerContentPreference
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+import org.mockito.Mockito
+import org.springframework.data.domain.PageImpl
+import org.springframework.data.domain.PageRequest
+
+class SeriesMainControllerTest {
+    private val contentSeriesService = Mockito.mock(ContentSeriesService::class.java)
+    private val bannerService = Mockito.mock(ContentSeriesBannerService::class.java)
+    private val langContext = LangContext().apply { setLang(Lang.JA) }
+    private val memberContentPreferenceService = Mockito.mock(MemberContentPreferenceService::class.java)
+    private val controller = SeriesMainController(
+        contentSeriesService = contentSeriesService,
+        bannerService = bannerService,
+        langContext = langContext,
+        memberContentPreferenceService = memberContentPreferenceService,
+        imageHost = "https://cdn.test"
+    )
+
+    @Test
+    fun shouldFetchOnlyRequestedLanguageBanners() {
+        val member = createMember(id = 1L)
+        val preference = ViewerContentPreference(
+            countryCode = "KR",
+            isAdultContentVisible = true,
+            contentType = ContentType.ALL,
+            isAdult = true
+        )
+        val pageable = PageRequest.of(0, 10)
+        val japaneseBanner = SeriesBanner(
+            imagePath = "banner/jp.png",
+            series = createSeries(id = 10L),
+            sortOrder = 1,
+            lang = Lang.JA
+        ).also {
+            it.id = 100L
+        }
+
+        Mockito.`when`(memberContentPreferenceService.resolveForQuery(member)).thenReturn(preference)
+        Mockito.`when`(bannerService.getDisplayBanners(pageable, Lang.JA))
+            .thenReturn(PageImpl(listOf(japaneseBanner), pageable, 1))
+        Mockito.`when`(
+            contentSeriesService.getSeriesList(
+                null,
+                false,
+                true,
+                true,
+                true,
+                ContentType.ALL,
+                member,
+                0,
+                20
+            )
+        ).thenReturn(GetSeriesListResponse(totalCount = 0, items = emptyList()))
+        Mockito.`when`(
+            contentSeriesService.getRecommendSeriesList(
+                true,
+                ContentType.ALL,
+                member
+            )
+        ).thenReturn(emptyList())
+
+        val response = controller.fetchData(member)
+
+        assertTrue(response.success)
+        assertEquals(1, response.data?.banners?.size)
+        assertEquals("series-10", response.data?.banners?.first()?.seriesTitle)
+        Mockito.verify(bannerService).getDisplayBanners(pageable, Lang.JA)
+        Mockito.verify(bannerService, Mockito.never()).getActiveBanners(pageable)
+    }
+
+    private fun createMember(id: Long): Member {
+        return Member(
+            email = "member-$id@test.com",
+            password = "password",
+            nickname = "member-$id"
+        ).also {
+            it.id = id
+        }
+    }
+
+    private fun createSeries(id: Long): Series {
+        return Series(
+            title = "series-$id",
+            introduction = "introduction-$id",
+            languageCode = "ja"
+        ).also {
+            it.id = id
+        }
+    }
+}
diff --git a/src/test/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/ContentSeriesBannerServiceTest.kt b/src/test/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/ContentSeriesBannerServiceTest.kt
new file mode 100644
index 00000000..ce77f408
--- /dev/null
+++ b/src/test/kotlin/kr/co/vividnext/sodalive/content/series/main/banner/ContentSeriesBannerServiceTest.kt
@@ -0,0 +1,100 @@
+package kr.co.vividnext.sodalive.content.series.main.banner
+
+import kr.co.vividnext.sodalive.admin.content.series.AdminContentSeriesRepository
+import kr.co.vividnext.sodalive.creator.admin.content.series.Series
+import kr.co.vividnext.sodalive.i18n.Lang
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import org.mockito.Mockito
+import org.springframework.data.domain.PageImpl
+import org.springframework.data.domain.PageRequest
+
+class ContentSeriesBannerServiceTest {
+    private lateinit var bannerRepository: SeriesBannerRepository
+    private lateinit var seriesRepository: AdminContentSeriesRepository
+    private lateinit var service: ContentSeriesBannerService
+
+    @BeforeEach
+    fun setUp() {
+        bannerRepository = Mockito.mock(SeriesBannerRepository::class.java)
+        seriesRepository = Mockito.mock(AdminContentSeriesRepository::class.java)
+        service = ContentSeriesBannerService(
+            bannerRepository = bannerRepository,
+            seriesRepository = seriesRepository
+        )
+    }
+
+    @Test
+    @DisplayName("일본어 배너 등록 요청은 JA 언어값으로 저장한다")
+    fun shouldRegisterJapaneseBanner() {
+        val series = createSeries(id = 1L)
+
+        Mockito.`when`(seriesRepository.findByIdAndActiveTrue(1L)).thenReturn(series)
+        Mockito.`when`(bannerRepository.findMaxSortOrder()).thenReturn(2)
+        Mockito.`when`(bannerRepository.save(Mockito.any(SeriesBanner::class.java))).thenAnswer { it.arguments[0] }
+
+        val banner = service.registerBanner(
+            seriesId = 1L,
+            imagePath = "banner/jp.png",
+            lang = Lang.JA
+        )
+
+        assertEquals(Lang.JA, banner.lang)
+        assertEquals(3, banner.sortOrder)
+        assertEquals("banner/jp.png", banner.imagePath)
+    }
+
+    @Test
+    @DisplayName("언어가 없는 배너 등록 요청은 KO로 저장한다")
+    fun shouldRegisterKoreanBannerWhenLangIsMissing() {
+        val series = createSeries(id = 2L)
+
+        Mockito.`when`(seriesRepository.findByIdAndActiveTrue(2L)).thenReturn(series)
+        Mockito.`when`(bannerRepository.findMaxSortOrder()).thenReturn(null)
+        Mockito.`when`(bannerRepository.save(Mockito.any(SeriesBanner::class.java))).thenAnswer { it.arguments[0] }
+
+        val banner = service.registerBanner(
+            seriesId = 2L,
+            imagePath = "banner/default.png",
+            lang = null
+        )
+
+        assertEquals(Lang.KO, banner.lang)
+        assertEquals(1, banner.sortOrder)
+    }
+
+    @Test
+    @DisplayName("일본어 사용자는 일본어 배너만 조회한다")
+    fun shouldReturnJapaneseBannersForJapaneseUser() {
+        val pageable = PageRequest.of(0, 10)
+        val japaneseBanner = SeriesBanner(
+            imagePath = "banner/jp.png",
+            series = createSeries(id = 3L),
+            sortOrder = 1,
+            lang = Lang.JA
+        )
+        val expectedPage = PageImpl(listOf(japaneseBanner), pageable, 1)
+
+        Mockito.`when`(bannerRepository.findByIsActiveTrueAndLangOrderBySortOrderAsc(Lang.JA, pageable))
+            .thenReturn(expectedPage)
+
+        val actual = service.getDisplayBanners(pageable, Lang.JA)
+
+        assertEquals(expectedPage, actual)
+        Mockito.verify(bannerRepository).findByIsActiveTrueAndLangOrderBySortOrderAsc(Lang.JA, pageable)
+        Mockito.verify(bannerRepository, Mockito.never())
+            .findByIsActiveTrueOrderBySortOrderAsc(pageable)
+    }
+
+    private fun createSeries(id: Long): Series {
+        return Series(
+            title = "series-$id",
+            introduction = "introduction-$id",
+            languageCode = "ko"
+        ).also {
+            it.id = id
+        }
+    }
+}