diff --git a/hideout/hideout-core/src/main/kotlin/dev/usbharu/hideout/core/config/MessageSourceConfig.kt b/hideout/hideout-core/src/main/kotlin/dev/usbharu/hideout/core/config/MessageSourceConfig.kt
index 73e2311c..efe82579 100644
--- a/hideout/hideout-core/src/main/kotlin/dev/usbharu/hideout/core/config/MessageSourceConfig.kt
+++ b/hideout/hideout-core/src/main/kotlin/dev/usbharu/hideout/core/config/MessageSourceConfig.kt
@@ -16,27 +16,17 @@
 
 package dev.usbharu.hideout.core.config
 
-import org.springframework.boot.autoconfigure.context.MessageSourceProperties
-import org.springframework.boot.context.properties.ConfigurationProperties
+import dev.usbharu.hideout.core.infrastructure.springframework.MergedPropertiesMessageSource
 import org.springframework.context.MessageSource
 import org.springframework.context.annotation.Bean
 import org.springframework.context.annotation.Configuration
 import org.springframework.context.annotation.Profile
-import org.springframework.context.support.ReloadableResourceBundleMessageSource
 
 @Configuration
 @Profile("dev")
 class MessageSourceConfig {
     @Bean
-    fun messageSource(messageSourceProperties: MessageSourceProperties): MessageSource {
-        val reloadableResourceBundleMessageSource = ReloadableResourceBundleMessageSource()
-        reloadableResourceBundleMessageSource.setBasename("classpath:" + messageSourceProperties.basename)
-        reloadableResourceBundleMessageSource.setCacheSeconds(0)
-        return reloadableResourceBundleMessageSource
+    fun messageSource(): MessageSource {
+        return MergedPropertiesMessageSource()
     }
-
-    @Bean
-    @Profile("dev")
-    @ConfigurationProperties(prefix = "spring.messages")
-    fun messageSourceProperties(): MessageSourceProperties = MessageSourceProperties()
 }
diff --git a/hideout/hideout-core/src/main/kotlin/dev/usbharu/hideout/core/infrastructure/springframework/MergedPropertiesMessageSource.kt b/hideout/hideout-core/src/main/kotlin/dev/usbharu/hideout/core/infrastructure/springframework/MergedPropertiesMessageSource.kt
new file mode 100644
index 00000000..d23a328d
--- /dev/null
+++ b/hideout/hideout-core/src/main/kotlin/dev/usbharu/hideout/core/infrastructure/springframework/MergedPropertiesMessageSource.kt
@@ -0,0 +1,60 @@
+package dev.usbharu.hideout.core.infrastructure.springframework
+
+import org.springframework.context.support.AbstractMessageSource
+import org.springframework.core.io.support.PathMatchingResourcePatternResolver
+import java.io.InputStreamReader
+import java.nio.charset.StandardCharsets
+import java.text.MessageFormat
+import java.util.*
+import java.util.concurrent.ConcurrentHashMap
+
+class MergedPropertiesMessageSource : AbstractMessageSource() {
+
+    private val messages: MutableMap<Locale, Properties> = ConcurrentHashMap()
+
+    init {
+        loadAllLocaleProperties("classpath*:/messages/hideout-web-messages*.properties")
+    }
+
+    private fun loadAllLocaleProperties(locationPattern: String) {
+        val resolver = PathMatchingResourcePatternResolver()
+        val resources = resolver.getResources(locationPattern)
+
+        for (resource in resources) {
+            val filename = resource.filename ?: continue
+
+            val localeSuffix = filename
+                .removePrefix("hideout-web-messages")
+                .removeSuffix(".properties")
+                .takeIf { it.isNotBlank() }
+                ?: "default"
+
+            val locale = if (localeSuffix == "default") {
+                Locale.ROOT
+            } else {
+                Locale.forLanguageTag(localeSuffix.replace('_', '-'))
+            }
+
+            val props = messages.getOrPut(locale) { Properties() }
+
+            resource.inputStream.use { stream ->
+                InputStreamReader(stream, StandardCharsets.UTF_8).use { reader ->
+                    val newProps = Properties()
+                    newProps.load(reader)
+                    props.putAll(newProps) // 上書きあり
+                }
+            }
+        }
+    }
+
+    override fun resolveCode(code: String, locale: Locale): MessageFormat? {
+        val props = messages[locale] ?: messages[Locale.ROOT] ?: return null
+        val msg = props.getProperty(code) ?: return null
+        return MessageFormat(msg, locale)
+    }
+
+    override fun resolveCodeWithoutArguments(code: String, locale: Locale): String? {
+        val props = messages[locale] ?: messages[Locale.ROOT] ?: return null
+        return props.getProperty(code)
+    }
+}
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