chore(#234): normalize Indonesian language code to "id"

app/src/main/java/com/brainwallet/data/source/MessagingTopicDataSource.kt

@@ -18,12 +18,29 @@ class MessagingTopicDataSource(
         )
     }
 
+    /**
+     * Note: Indonesian language code is normalized from "in" to "id" to maintain
+     * consistency with backend batch messaging server which uses ISO 639-1 standard.
+     * Supports both "in" and "id" as input for Indonesian language.
+     */
     private fun getBaseLanguageCode(languageCode: String): String {
         val normalizedLanguageCode = languageCode.split("_", "-").first().lowercase()
+
+        // Handle reverse mapping: if "id" is passed, treat it as Indonesian
+        val searchCode = when (normalizedLanguageCode) {
+            "id" -> "in"
+            else -> normalizedLanguageCode
+        }
+
         val targetLanguage = supportedLanguages.find { 
-            it.code.split("-").first().lowercase() == normalizedLanguageCode 
+            it.code.split("-").first().lowercase() == searchCode 
         } ?: defaultLanguage
 
-        return targetLanguage.code.split("-").first().lowercase()
+        val baseCode = targetLanguage.code.split("-").first().lowercase()
+
+        return when (baseCode) {
+            "in" -> "id"
+            else -> baseCode
+        }
     }
 }

app/src/test/java/com/brainwallet/data/source/MessagingTopicDataSourceTest.kt

@@ -1,6 +1,5 @@
 package com.brainwallet.data.source
 
-import com.brainwallet.data.model.Language
 import org.junit.Before
 import org.junit.Test
 
@@ -72,12 +71,45 @@ class MessagingTopicDataSourceTest {
         }
     }
 
+    @Test
+    fun `given Indonesian language code when getTopicsByLanguageCode called then it should normalize to id for backend consistency`() {
+        val result = dataSource.getTopicsByLanguageCode("in")
+
+        val expectedTopics = listOf("initial_id", "news_id", "promo_id", "warn_id")
+        assert(result == expectedTopics) {
+            "Expected Indonesian language code 'in' to be normalized to 'id' for backend consistency but got $result"
+        }
+    }
+
+    @Test
+    fun `given Indonesian locale with region when getTopicsByLanguageCode called then it should normalize to id`() {
+        val result = dataSource.getTopicsByLanguageCode("in_ID")
+
+        val expectedTopics = listOf("initial_id", "news_id", "promo_id", "warn_id")
+        assert(result == expectedTopics) {
+            "Expected Indonesian locale 'in_ID' to be normalized to 'id' for backend consistency but got $result"
+        }
+    }
+
+    @Test
+    fun `given id language code when getTopicsByLanguageCode called then it should be recognized as Indonesian`() {
+        val result = dataSource.getTopicsByLanguageCode("id")
+
+        val expectedTopics = listOf("initial_id", "news_id", "promo_id", "warn_id")
+        assert(result == expectedTopics) {
+            "Expected 'id' language code to be recognized as Indonesian and return Indonesian topics but got $result"
+        }
+    }
+
     @Test
     fun `given all supported languages when getTopicsByLanguageCode called then it should return correct base language topics`() {
         val testCases = mapOf(
             "en" to "en",
-            "es" to "es", 
-            "in" to "in",
+            "es" to "es",
+            // Check All possible indonesian combination
+            "in" to "id",
+            "in_ID" to "id",
+            "id" to "id",
             "ar" to "ar",
             "uk" to "uk",
             "ru" to "ru",