[CHA-5060] feat: support multiple auto-translation languages

docs/features/translation.md

@@ -104,14 +104,26 @@ Channel.update("channeltype", "channelid")
   .data(ChannelRequestObject
     .builder()
     .autoTranslationEnabled(true)
-    .autoTranslationLanguage(Language.EN)
+    .autoTranslationLanguages(List.of(Language.EN))
+    .build())
+  .request();
+
+// translate messages into up to five languages
+Channel.update("channeltype", "channelid")
+  .data(ChannelRequestObject
+    .builder()
+    .autoTranslationEnabled(true)
+    .autoTranslationLanguages(List.of(Language.EN, Language.FR, Language.IT))
     .build())
   .request();
 
 // auto translate messages for all channels
 App.update().autoTranslationEnabled(true).request();
 ```
 
+> [!NOTE]
+> `autoTranslationLanguages` accepts up to five languages and can only be set on channel create or full update. Partial update rejects `auto_translation_language` as a reserved field. The single language `autoTranslationLanguage(Language)` setter is deprecated: calling it more than once keeps only the last language.
+
 ### Set user language
 
 In order for auto translation to work, you must set the user language or specify a destination language for the channel using the `auto_translation_language` field (see previous code example).

src/main/java/io/getstream/chat/java/models/Channel.java

@@ -30,10 +30,12 @@
 import io.getstream.chat.java.models.framework.StreamResponseObject;
 import io.getstream.chat.java.services.ChannelService;
 import io.getstream.chat.java.services.framework.Client;
+import java.util.Collections;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.stream.Collectors;
 import lombok.*;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -272,9 +274,32 @@ public static class ChannelRequestObject {
     @JsonProperty("auto_translation_enabled")
     private Boolean autoTranslationEnabled;
 
+    /**
+     * @deprecated the backend accepts up to five languages, use {@code
+     *     autoTranslationLanguages(List)} instead.
+     */
+    @Nullable @Deprecated @JsonIgnore private Language autoTranslationLanguage;
+
+    /** Up to five languages. Can only be set on channel create or full update. */
+    @Nullable @JsonIgnore private List<Language> autoTranslationLanguages;
+
     @Nullable
     @JsonProperty("auto_translation_language")
-    private Language autoTranslationLanguage;
+    public String getAutoTranslationLanguageValue() {
+      List<Language> languages = autoTranslationLanguages;
+      if (languages == null && autoTranslationLanguage != null) {
+        languages = Collections.singletonList(autoTranslationLanguage);
+      }
+      if (languages == null) {
+        return null;
+      }
+      String value =
+          languages.stream()
+              .filter(language -> language != null && language != Language.UNKNOWN)
+              .map(Language::getValue)
+              .collect(Collectors.joining(","));
+      return value.isEmpty() ? null : value;
+    }
 
     @Nullable
     @JsonProperty("frozen")
@@ -321,6 +346,7 @@ private ChannelRequestObject(
         @Nullable String team,
         @Nullable Boolean autoTranslationEnabled,
         @Nullable Language autoTranslationLanguage,
+        @Nullable List<Language> autoTranslationLanguages,
         @Nullable Boolean frozen,
         @Nullable List<ChannelMemberRequestObject> members,
         @Nullable List<ChannelMemberRequestObject> invites,
@@ -331,6 +357,7 @@ private ChannelRequestObject(
       this.team = team;
       this.autoTranslationEnabled = autoTranslationEnabled;
       this.autoTranslationLanguage = autoTranslationLanguage;
+      this.autoTranslationLanguages = autoTranslationLanguages;
       this.frozen = frozen;
       this.members = members;
       this.invites = invites;

src/main/java/io/getstream/chat/java/models/Language.java

@@ -117,5 +117,17 @@ public enum Language {
   @JsonProperty("zh-TW")
   ZH_TW,
   @JsonEnumDefaultValue
-  UNKNOWN
+  UNKNOWN;
+
+  /**
+   * @return the value sent over the wire, e.g. {@code "es-MX"} for {@link Language#ES_MX}
+   */
+  public String getValue() {
+    try {
+      JsonProperty jsonProperty = Language.class.getField(name()).getAnnotation(JsonProperty.class);
+      return jsonProperty == null ? name() : jsonProperty.value();
+    } catch (NoSuchFieldException e) {
+      throw new IllegalStateException("Unknown language constant " + name(), e);
+    }
+  }
 }

src/test/java/io/getstream/chat/java/ChannelAutoTranslationLanguageTest.java

@@ -0,0 +1,98 @@
+package io.getstream.chat.java;
+
+import com.fasterxml.jackson.annotation.JsonAutoDetect;
+import com.fasterxml.jackson.annotation.PropertyAccessor;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.getstream.chat.java.models.Channel.ChannelRequestObject;
+import io.getstream.chat.java.models.Language;
+import java.util.Arrays;
+import java.util.Collections;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+public class ChannelAutoTranslationLanguageTest {
+
+  // Mirrors the visibility configuration of DefaultClient's mapper.
+  private static final ObjectMapper MAPPER =
+      new ObjectMapper()
+          .setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.NONE)
+          .setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
+
+  @DisplayName("Multiple languages serialize as a comma separated list")
+  @Test
+  void whenSettingLanguages_thenSerializedAsCommaSeparatedList() throws Exception {
+    ChannelRequestObject channel =
+        ChannelRequestObject.builder()
+            .autoTranslationEnabled(true)
+            .autoTranslationLanguages(Arrays.asList(Language.IT, Language.FR, Language.ES_MX))
+            .build();
+
+    Assertions.assertEquals("it,fr,es-MX", channel.getAutoTranslationLanguageValue());
+    Assertions.assertTrue(
+        MAPPER
+            .writeValueAsString(channel)
+            .contains("\"auto_translation_language\":\"it,fr,es-MX\""));
+  }
+
+  @DisplayName("Single language setter keeps working")
+  @Test
+  void whenSettingSingleLanguage_thenSerializedAsSingleValue() throws Exception {
+    @SuppressWarnings("deprecation")
+    ChannelRequestObject channel =
+        ChannelRequestObject.builder().autoTranslationLanguage(Language.IT).build();
+
+    Assertions.assertTrue(
+        MAPPER.writeValueAsString(channel).contains("\"auto_translation_language\":\"it\""));
+  }
+
+  @DisplayName("The language list wins over the single language")
+  @Test
+  void whenSettingBoth_thenListWins() {
+    @SuppressWarnings("deprecation")
+    ChannelRequestObject channel =
+        ChannelRequestObject.builder()
+            .autoTranslationLanguage(Language.IT)
+            .autoTranslationLanguages(Collections.singletonList(Language.FR))
+            .build();
+
+    Assertions.assertEquals("fr", channel.getAutoTranslationLanguageValue());
+  }
+
+  @DisplayName("An empty list serializes as null")
+  @Test
+  void whenSettingEmptyList_thenSerializedAsNull() throws Exception {
+    ChannelRequestObject channel =
+        ChannelRequestObject.builder().autoTranslationLanguages(Collections.emptyList()).build();
+
+    Assertions.assertNull(channel.getAutoTranslationLanguageValue());
+    Assertions.assertTrue(
+        MAPPER.writeValueAsString(channel).contains("\"auto_translation_language\":null"));
+  }
+
+  @DisplayName("Null and unknown languages are dropped")
+  @Test
+  void whenListHoldsNullOrUnknown_thenTheyAreDropped() {
+    ChannelRequestObject channel =
+        ChannelRequestObject.builder()
+            .autoTranslationLanguages(Arrays.asList(Language.EN, null, Language.UNKNOWN))
+            .build();
+
+    Assertions.assertEquals("en", channel.getAutoTranslationLanguageValue());
+    Assertions.assertNull(
+        ChannelRequestObject.builder()
+            .autoTranslationLanguages(Arrays.asList(null, Language.UNKNOWN))
+            .build()
+            .getAutoTranslationLanguageValue());
+  }
+
+  @DisplayName("No language set serializes as null")
+  @Test
+  void whenSettingNoLanguage_thenSerializedAsNull() throws Exception {
+    ChannelRequestObject channel = ChannelRequestObject.builder().build();
+
+    Assertions.assertNull(channel.getAutoTranslationLanguageValue());
+    Assertions.assertTrue(
+        MAPPER.writeValueAsString(channel).contains("\"auto_translation_language\":null"));
+  }
+}

src/test/java/io/getstream/chat/java/LanguageTest.java

@@ -0,0 +1,25 @@
+package io.getstream.chat.java;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import io.getstream.chat.java.models.Language;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+public class LanguageTest {
+
+  @DisplayName("Every language returns its declared wire value")
+  @Test
+  void whenReadingValue_thenItMatchesTheDeclaredJsonProperty() throws Exception {
+    for (Language language : Language.values()) {
+      JsonProperty jsonProperty =
+          Language.class.getField(language.name()).getAnnotation(JsonProperty.class);
+      if (language == Language.UNKNOWN) {
+        Assertions.assertNull(jsonProperty);
+        continue;
+      }
+      Assertions.assertNotNull(jsonProperty, language.name() + " is missing @JsonProperty");
+      Assertions.assertEquals(jsonProperty.value(), language.getValue());
+    }
+  }
+}