Use locale-aware collation when sorting recipients in message details.

app/src/main/java/org/thoughtcrime/securesms/groups/ui/GroupMemberOrder.kt

@@ -29,6 +29,18 @@ object GroupMemberOrder {
     getDisplayName: (T) -> String
   ): Comparator<T> = compareBy<T> { !isSelf(it) }
     .thenBy { !isAdmin(it) }
-    .thenBy { !hasDisplayName(it) }
+    .then(displayNameComparator(hasDisplayName, getDisplayName))
+
+  /**
+   * Creates a [Comparator] for just the display-name portion of the canonical order: members with a user-set display name
+   * first, then alphabetically by display name using locale-aware collation.
+   *
+   * Useful for member lists that have no notion of self-first or admin-first ordering.
+   */
+  @JvmStatic
+  fun <T> displayNameComparator(
+    hasDisplayName: (T) -> Boolean,
+    getDisplayName: (T) -> String
+  ): Comparator<T> = compareBy<T> { !hasDisplayName(it) }
     .thenBy { collator.getCollationKey(getDisplayName(it)) }
 }

app/src/main/java/org/thoughtcrime/securesms/messagedetails/MessageDetails.java

@@ -5,6 +5,7 @@ import androidx.annotation.NonNull;
 
 import org.thoughtcrime.securesms.conversation.ConversationMessage;
 import org.thoughtcrime.securesms.dependencies.AppDependencies;
+import org.thoughtcrime.securesms.groups.ui.GroupMemberOrder;
 
 import java.util.Collection;
 import java.util.Comparator;
@@ -12,9 +13,9 @@ import java.util.List;
 import java.util.TreeSet;
 
 public final class MessageDetails {
-  private static final Comparator<RecipientDeliveryStatus> HAS_DISPLAY_NAME     = (r1, r2) -> Boolean.compare(r2.getRecipient().hasAUserSetDisplayName(AppDependencies.getApplication()), r1.getRecipient().hasAUserSetDisplayName(AppDependencies.getApplication()));
-  private static final Comparator<RecipientDeliveryStatus> ALPHABETICAL         = (r1, r2) -> r1.getRecipient().getDisplayName(AppDependencies.getApplication()).compareToIgnoreCase(r2.getRecipient().getDisplayName(AppDependencies.getApplication()));
-  private static final Comparator<RecipientDeliveryStatus> RECIPIENT_COMPARATOR = HAS_DISPLAY_NAME.thenComparing(ALPHABETICAL);
+  private static final Comparator<RecipientDeliveryStatus> RECIPIENT_COMPARATOR = GroupMemberOrder.<RecipientDeliveryStatus>displayNameComparator(r -> r.getRecipient().hasAUserSetDisplayName(AppDependencies.getApplication()),
+                                                                                                                                                r -> r.getRecipient().getDisplayName(AppDependencies.getApplication()))
+                                                                                                 .thenComparing(r -> r.getRecipient().getId());
 
   private final ConversationMessage conversationMessage;
 

app/src/test/java/org/thoughtcrime/securesms/groups/ui/GroupMemberOrderTest.kt

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2026 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.groups.ui
+
+import assertk.assertThat
+import assertk.assertions.isEqualTo
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import java.util.Locale
+
+class GroupMemberOrderTest {
+
+  private lateinit var previousLocale: Locale
+
+  @Before
+  fun setUp() {
+    previousLocale = Locale.getDefault()
+    Locale.setDefault(Locale.GERMANY)
+  }
+
+  @After
+  fun tearDown() {
+    Locale.setDefault(previousLocale)
+  }
+
+  @Test
+  fun `displayNameComparator - accented names sort alongside their unaccented equivalents`() {
+    val names = listOf("Zeta", "Ärzte", "Anna", "Émile", "Bernd", "Ökonom", "Oskar")
+
+    val sorted = names.sortedWith(GroupMemberOrder.displayNameComparator({ true }, { it }))
+
+    assertThat(sorted).isEqualTo(listOf("Anna", "Ärzte", "Bernd", "Émile", "Ökonom", "Oskar", "Zeta"))
+  }
+
+  @Test
+  fun `comparator - self first, then admins, then named members alphabetically`() {
+    val self = Member("Zoe", isSelf = true)
+    val admin = Member("Yannick", isAdmin = true)
+    val bernd = Member("Bernd")
+    val arzte = Member("Ärzte")
+    val unnamed = Member("+15551234567", hasDisplayName = false)
+
+    val sorted = listOf(bernd, unnamed, arzte, admin, self).sortedWith(MEMBER_ORDER)
+
+    assertThat(sorted).isEqualTo(listOf(self, admin, arzte, bernd, unnamed))
+  }
+
+  private data class Member(
+    val name: String,
+    val isSelf: Boolean = false,
+    val isAdmin: Boolean = false,
+    val hasDisplayName: Boolean = true
+  )
+
+  companion object {
+    private val MEMBER_ORDER = GroupMemberOrder.comparator<Member>({ it.isSelf }, { it.isAdmin }, { it.hasDisplayName }, { it.name })
+  }
+}