[messaging]: Inconsistent behavior of FCM notification localization between Android and iOS

[LuigiFiorillo]

Is there an existing issue for this?

• I have searched the existing issues.

Which plugins are affected?

Messaging

Which platforms are affected?

Android

Description

Description

When sending a Firebase Cloud Messaging notification with both localization keys (title_loc_key / body_loc_key) and fallback text (title / body):

• On iOS, the system correctly uses the localization keys if they exist, falling back to the text only if the key is missing.
• On Android, the system always displays the title / body text if present, ignoring the localization keys entirely.

Notes

This difference can cause inconsistent user experience across platforms for localized notifications. Workarounds require removing the fallback text on Android or handling notifications manually in the app.

Reproducing the issue

Steps to Reproduce

1. Send a FCM message with both title / body and title_loc_key / body_loc_key.
2. Observe that Android shows the title / body text, while iOS shows the localized string.

Expected Behavior

Android should behave like iOS and prioritize the localization keys if present.

Firebase Core version

4.1.1

Flutter Version

3.3.0

Relevant Log Output

Flutter dependencies

Expand Flutter dependencies snippet

Dart SDK 3.9.0
Flutter SDK 3.35.1
wallet_app_sturcio 0.5.8+54

dependencies:
- app_links 6.4.1 [flutter app_links_linux app_links_platform_interface app_links_web]
- barcode 2.2.9 [meta qr]
- base_x 2.0.1
- basic_utils 5.8.2 [http logging json_annotation pointycastle archive]
- bluetooth_low_energy 6.1.0 [flutter bluetooth_low_energy_platform_interface bluetooth_low_energy_android bluetooth_low_energy_darwin bluetooth_low_energy_windows bluetooth_low_energy_linux]
- cached_network_image 3.4.1 [cached_network_image_platform_interface cached_network_image_web flutter flutter_cache_manager octo_image]
- cbor 6.3.7 [collection typed_data hex convert ieee754 meta characters]
- cloud_firestore 6.0.0 [cloud_firestore_platform_interface cloud_firestore_web collection firebase_core firebase_core_platform_interface flutter meta]
- connectivity_plus 6.1.5 [flutter flutter_web_plugins connectivity_plus_platform_interface web meta nm collection]
- convert 3.1.2 [typed_data]
- crypto_keys_plus 0.5.0 [pointycastle meta collection]
- cupertino_icons 1.0.8
- dart_jsonwebtoken 3.2.0 [pointycastle convert ed25519_edwards clock]
- device_info_plus 11.5.0 [device_info_plus_platform_interface ffi file flutter flutter_web_plugins meta web win32 win32_registry]
- downloadsfolder 1.2.0 [flutter plugin_platform_interface path_provider path diacritic dartx]
- file_picker 10.3.1 [flutter flutter_web_plugins flutter_plugin_android_lifecycle plugin_platform_interface ffi path win32 cross_file web dbus]
- firebase_analytics 12.0.0 [firebase_analytics_platform_interface firebase_analytics_web firebase_core firebase_core_platform_interface flutter]
- firebase_core 4.0.0 [firebase_core_platform_interface firebase_core_web flutter meta]
- firebase_crashlytics 5.0.0 [firebase_core firebase_core_platform_interface firebase_crashlytics_platform_interface flutter stack_trace]
- firebase_messaging 16.0.0 [firebase_core firebase_core_platform_interface firebase_messaging_platform_interface firebase_messaging_web flutter meta]
- firebase_storage 13.0.0 [firebase_core firebase_core_platform_interface firebase_storage_platform_interface firebase_storage_web flutter]
- flutter 0.0.0 [characters collection material_color_utilities meta vector_math sky_engine]
- flutter_inappwebview 6.1.5 [flutter flutter_inappwebview_platform_interface flutter_inappwebview_android flutter_inappwebview_ios flutter_inappwebview_macos flutter_inappwebview_web flutter_inappwebview_windows]
- flutter_local_notifications 19.4.0 [clock flutter flutter_local_notifications_linux flutter_local_notifications_windows flutter_local_notifications_platform_interface timezone]
- flutter_localizations 0.0.0 [flutter intl path]
- flutter_lucide_icons 0.539.0 [flutter flutter_svg]
- flutter_native_splash 2.4.6 [args flutter flutter_web_plugins html image meta path universal_io xml yaml ansicolor]
- flutter_riverpod 2.6.1 [collection flutter meta riverpod state_notifier]
- flutter_secure_storage 9.2.4 [flutter flutter_secure_storage_linux flutter_secure_storage_macos flutter_secure_storage_platform_interface flutter_secure_storage_web flutter_secure_storage_windows meta]
- flutter_svg 2.2.0 [flutter http vector_graphics vector_graphics_codec vector_graphics_compiler]
- freezed_annotation 3.1.0 [collection json_annotation meta]
- get 4.7.2 [flutter web]
- go_router 16.1.0 [collection flutter flutter_web_plugins logging meta]
- http 1.5.0 [async http_parser meta web]
- http_parser 4.1.2 [collection source_span string_scanner typed_data]
- intl 0.20.2 [clock meta path]
- iso_mdoc 1.6.0 [convert cbor ed25519_edwards x25519 pointycastle]
- jailbreak_root_detection 1.1.6 [flutter]
- jose_plus 0.4.7 [crypto_keys_plus meta typed_data x509_plus http http_parser asn1lib clock]
- json_annotation 4.9.0 [meta]
- json_path 0.7.6 [iregexp maybe_just_nothing petitparser rfc_6901]
- local_auth 2.3.0 [flutter local_auth_android local_auth_darwin local_auth_platform_interface local_auth_windows]
- logging 1.3.0
- lottie 3.3.1 [archive flutter http path vector_math]
- mobile_scanner 7.0.1 [collection flutter flutter_web_plugins meta plugin_platform_interface web]
- objectbox 4.3.0 [collection flat_buffers ffi meta path]
- objectbox_flutter_libs 4.3.0 [flutter objectbox path_provider]
- open_file 3.5.10 [flutter open_file_android open_file_web open_file_ios open_file_mac open_file_windows open_file_linux open_file_platform_interface]
- otp_pin_field 1.4.1 [flutter flutter_web_plugins plugin_platform_interface universal_html]
- package_info_plus 8.3.1 [ffi flutter flutter_web_plugins http meta path package_info_plus_platform_interface web win32 clock]
- path 1.9.1
- path_provider 2.1.5 [flutter path_provider_android path_provider_foundation path_provider_linux path_provider_platform_interface path_provider_windows]
- permission_handler 12.0.1 [flutter meta permission_handler_android permission_handler_apple permission_handler_html permission_handler_windows permission_handler_platform_interface]
- pointycastle 4.0.0 [collection convert]
- rive 0.13.20 [collection flutter flutter_web_plugins http meta plugin_platform_interface rive_common]
- riverpod_annotation 2.6.1 [meta riverpod]
- shared_preferences 2.5.3 [flutter shared_preferences_android shared_preferences_foundation shared_preferences_linux shared_preferences_platform_interface shared_preferences_web shared_preferences_windows]
- syncfusion_flutter_pdfviewer 31.1.21 [flutter web http uuid async vector_math url_launcher intl device_info_plus syncfusion_pdfviewer_platform_interface syncfusion_pdfviewer_web syncfusion_pdfviewer_macos syncfusion_pdfviewer_windows syncfusion_pdfviewer_linux syncfusion_flutter_core syncfusion_flutter_pdf syncfusion_flutter_signaturepad]
- tutorial_coach_mark 1.3.1 [flutter]
- typed_data 1.4.0 [collection]
- url_launcher 6.3.2 [flutter url_launcher_android url_launcher_ios url_launcher_linux url_launcher_macos url_launcher_platform_interface url_launcher_web url_launcher_windows]
- uuid 4.5.1 [crypto sprintf meta fixnum]
- vibration 3.1.3 [flutter plugin_platform_interface vibration_platform_interface]
- x25519 0.1.1 [collection adaptive_number]
- x509_plus 0.3.3 [asn1lib collection crypto_keys_plus]

dev dependencies:
- build_runner 2.5.4 [analyzer args async build build_config build_daemon build_resolvers build_runner_core code_builder collection crypto dart_style frontend_server_client glob graphs http http_multi_server io js logging meta mime package_config path pool pub_semver pubspec_parse shelf shelf_web_socket stack_trace stream_transform timing watcher web web_socket_channel yaml]
- custom_lint 0.7.6 [analyzer analyzer_plugin args async ci cli_util collection custom_lint_core freezed_annotation json_annotation meta package_config path pub_semver pubspec_parse rxdart uuid yaml]
- flutter_launcher_icons 0.14.4 [args checked_yaml cli_util image json_annotation path yaml]
- flutter_lints 6.0.0 [lints]
- flutter_test 0.0.0 [flutter test_api matcher path fake_async clock stack_trace vector_math leak_tracker_flutter_testing collection meta stream_channel]
- freezed 3.1.0 [analyzer build build_config collection meta source_gen freezed_annotation json_annotation dart_style pub_semver]
- json_serializable 6.9.5 [analyzer async build build_config collection dart_style json_annotation meta path pub_semver pubspec_parse source_gen source_helper]
- mockito 5.4.6 [analyzer build code_builder collection dart_style matcher meta path source_gen test_api]
- mocktail_image_network 1.2.0 [mocktail]
- objectbox_generator 4.3.0 [objectbox analyzer build collection dart_style glob path source_gen pubspec_parse yaml http pointycastle]
- rename_app 1.6.5 [flutter xml]
- riverpod_generator 2.6.5 [analyzer build build_config collection crypto meta path riverpod_analyzer_utils riverpod_annotation source_gen]
- riverpod_lint 2.6.5 [analyzer analyzer_plugin collection custom_lint_builder meta path riverpod riverpod_analyzer_utils source_span yaml]

transitive dependencies:
- _fe_analyzer_shared 85.0.0 [meta]
- _flutterfire_internals 1.3.60 [collection firebase_core firebase_core_platform_interface flutter meta]
- adaptive_number 1.0.0 [fixnum]
- analyzer 7.6.0 [_fe_analyzer_shared collection convert crypto glob meta package_config path pub_semver source_span watcher yaml]
- analyzer_plugin 0.13.4 [analyzer collection dart_style pub_semver yaml path]
- ansicolor 2.0.3
- app_links_linux 1.0.3 [flutter app_links_platform_interface gtk]
- app_links_platform_interface 2.0.2 [flutter plugin_platform_interface]
- app_links_web 1.0.4 [flutter flutter_web_plugins app_links_platform_interface web]
- archive 4.0.7 [crypto path posix]
- args 2.7.0
- asn1lib 1.6.5
- async 2.13.0 [collection meta]
- bluetooth_low_energy_android 6.1.0 [flutter bluetooth_low_energy_platform_interface collection]
- bluetooth_low_energy_darwin 6.1.0 [flutter bluetooth_low_energy_platform_interface]
- bluetooth_low_energy_linux 6.1.0 [flutter bluetooth_low_energy_platform_interface bluez]
- bluetooth_low_energy_platform_interface 6.1.0 [flutter plugin_platform_interface hybrid_logging]
- bluetooth_low_energy_windows 6.1.0 [flutter bluetooth_low_energy_platform_interface]
- bluez 0.8.3 [dbus]
- boolean_selector 2.1.2 [source_span string_scanner]
- build 2.5.4 [analyzer async build_runner_core built_collection built_value convert crypto glob graphs logging meta package_config path pool]
- build_config 1.1.2 [checked_yaml json_annotation path pubspec_parse yaml]
- build_daemon 4.0.4 [built_collection built_value crypto http_multi_server logging path pool shelf shelf_web_socket stream_transform watcher web_socket_channel]
- build_resolvers 2.5.4 [analyzer async build build_runner_core collection convert crypto graphs logging package_config path pool pub_semver stream_transform]
- build_runner_core 9.1.2 [analyzer async build build_config build_resolvers build_runner built_collection built_value collection convert crypto glob graphs json_annotation logging meta package_config path pool timing watcher yaml]
- built_collection 5.1.1
- built_value 8.11.1 [built_collection collection fixnum meta]
- cached_network_image_platform_interface 4.1.1 [flutter flutter_cache_manager]
- cached_network_image_web 1.3.1 [cached_network_image_platform_interface flutter flutter_cache_manager web]
- characters 1.4.0
- charcode 1.4.0
- checked_yaml 2.0.4 [json_annotation source_span yaml]
- ci 0.1.0
- cli_util 0.4.2 [meta path]
- clock 1.1.2
- cloud_firestore_platform_interface 7.0.0 [_flutterfire_internals collection firebase_core flutter meta plugin_platform_interface]
- cloud_firestore_web 5.0.0 [_flutterfire_internals cloud_firestore_platform_interface collection firebase_core firebase_core_web flutter flutter_web_plugins]
- code_builder 4.10.1 [built_collection built_value collection matcher meta]
- collection 1.19.1
- connectivity_plus_platform_interface 2.0.1 [flutter meta plugin_platform_interface]
- cross_file 0.3.4+2 [meta web]
- crypto 3.0.6 [typed_data]
- csslib 1.0.2 [source_span]
- custom_lint_builder 0.7.6 [analyzer analyzer_plugin collection custom_lint custom_lint_core custom_lint_visitor glob hotreloader meta package_config path pubspec_parse rxdart]
- custom_lint_core 0.7.5 [analyzer analyzer_plugin collection custom_lint_visitor glob matcher meta package_config path pubspec_parse source_span uuid yaml]
- custom_lint_visitor 1.0.0+7.7.0 [analyzer]
- dart_style 3.1.1 [analyzer args collection package_config path pub_semver source_span yaml]
- dartx 1.2.0 [characters collection crypto meta path time]
- dbus 0.7.11 [args ffi meta xml]
- device_info_plus_platform_interface 7.0.3 [flutter meta plugin_platform_interface]
- diacritic 0.1.6
- ed25519_edwards 0.3.1 [collection crypto convert adaptive_number]
- fake_async 1.3.3 [clock collection]
- ffi 2.1.4
- file 7.0.1 [meta path]
- firebase_analytics_platform_interface 5.0.0 [_flutterfire_internals firebase_core flutter meta plugin_platform_interface]
- firebase_analytics_web 0.6.0 [_flutterfire_internals firebase_analytics_platform_interface firebase_core firebase_core_web flutter flutter_web_plugins]
- firebase_core_platform_interface 6.0.0 [collection flutter flutter_test meta plugin_platform_interface]
- firebase_core_web 3.0.0 [firebase_core_platform_interface flutter flutter_web_plugins meta web]
- firebase_crashlytics_platform_interface 3.8.11 [_flutterfire_internals collection firebase_core flutter meta plugin_platform_interface]
- firebase_messaging_platform_interface 4.7.0 [_flutterfire_internals firebase_core flutter meta plugin_platform_interface]
- firebase_messaging_web 4.0.0 [_flutterfire_internals firebase_core firebase_core_web firebase_messaging_platform_interface flutter flutter_web_plugins meta web]
- firebase_storage_platform_interface 5.2.11 [_flutterfire_internals collection firebase_core flutter meta plugin_platform_interface]
- firebase_storage_web 3.10.18 [_flutterfire_internals async firebase_core firebase_core_web firebase_storage_platform_interface flutter flutter_web_plugins http meta web]
- fixnum 1.1.1
- flat_buffers 23.5.26
- flutter_cache_manager 3.4.1 [clock collection file flutter http path path_provider rxdart sqflite uuid]
- flutter_inappwebview_android 1.1.3 [flutter flutter_inappwebview_platform_interface]
- flutter_inappwebview_internal_annotations 1.2.0
- flutter_inappwebview_ios 1.1.2 [flutter flutter_inappwebview_platform_interface]
- flutter_inappwebview_macos 1.1.2 [flutter flutter_inappwebview_platform_interface]
- flutter_inappwebview_platform_interface 1.3.0+1 [flutter flutter_inappwebview_internal_annotations plugin_platform_interface]
- flutter_inappwebview_web 1.1.2 [flutter flutter_web_plugins web flutter_inappwebview_platform_interface]
- flutter_inappwebview_windows 0.6.0 [flutter flutter_inappwebview_platform_interface]
- flutter_local_notifications_linux 6.0.0 [dbus ffi flutter flutter_local_notifications_platform_interface path xdg_directories]
- flutter_local_notifications_platform_interface 9.1.0 [plugin_platform_interface]
- flutter_local_notifications_windows 1.0.2 [flutter ffi flutter_local_notifications_platform_interface meta timezone xml]
- flutter_plugin_android_lifecycle 2.0.29 [flutter]
- flutter_secure_storage_linux 1.2.3 [flutter flutter_secure_storage_platform_interface]
- flutter_secure_storage_macos 3.1.3 [flutter flutter_secure_storage_platform_interface]
- flutter_secure_storage_platform_interface 1.1.2 [flutter plugin_platform_interface]
- flutter_secure_storage_web 1.2.1 [flutter flutter_secure_storage_platform_interface flutter_web_plugins js]
- flutter_secure_storage_windows 3.1.2 [ffi flutter flutter_secure_storage_platform_interface path path_provider win32]
- flutter_web_plugins 0.0.0 [flutter]
- frontend_server_client 4.0.0 [async path]
- glob 2.1.3 [async collection file path string_scanner]
- graphs 2.3.2 [collection]
- gtk 2.1.0 [ffi flutter meta]
- hex 0.2.0
- hotreloader 4.3.0 [collection logging path stream_transform vm_service watcher]
- html 0.15.6 [csslib source_span]
- http_multi_server 3.2.2 [async]
- hybrid_logging 1.0.0 [logging]
- ieee754 1.0.3 [meta]
- image 4.5.4 [archive meta xml]
- io 1.0.5 [meta path string_scanner]
- iregexp 0.1.2 [petitparser]
- js 0.6.7 [meta]
- leak_tracker 11.0.1 [clock collection meta path vm_service]
- leak_tracker_flutter_testing 3.0.10 [flutter leak_tracker leak_tracker_testing matcher meta]
- leak_tracker_testing 3.0.2 [leak_tracker matcher meta]
- lints 6.0.0
- local_auth_android 1.0.51 [flutter flutter_plugin_android_lifecycle intl local_auth_platform_interface]
- local_auth_darwin 1.6.0 [flutter intl local_auth_platform_interface]
- local_auth_platform_interface 1.0.10 [flutter plugin_platform_interface]
- local_auth_windows 1.0.11 [flutter local_auth_platform_interface]
- matcher 0.12.17 [async meta stack_trace term_glyph test_api]
- material_color_utilities 0.11.1 [collection]
- maybe_just_nothing 0.5.3
- meta 1.16.0
- mime 2.0.0
- mocktail 1.0.4 [collection matcher test_api]
- nm 0.5.0 [dbus]
- octo_image 2.1.0 [flutter]
- open_file_android 1.0.6 [flutter open_file_platform_interface]
- open_file_ios 1.0.3 [flutter open_file_platform_interface]
- open_file_linux 0.0.5 [flutter ffi open_file_platform_interface]
- open_file_mac 1.0.3 [flutter open_file_platform_interface]
- open_file_platform_interface 1.0.3 [flutter plugin_platform_interface]
- open_file_web 0.0.4 [flutter flutter_web_plugins open_file_platform_interface web]
- open_file_windows 0.0.3 [flutter ffi open_file_platform_interface]
- package_config 2.2.0 [path]
- package_info_plus_platform_interface 3.2.1 [flutter meta plugin_platform_interface]
- path_parsing 1.1.0 [meta vector_math]
- path_provider_android 2.2.17 [flutter path_provider_platform_interface]
- path_provider_foundation 2.4.2 [flutter path_provider_platform_interface]
- path_provider_linux 2.2.1 [ffi flutter path path_provider_platform_interface xdg_directories]
- path_provider_platform_interface 2.1.2 [flutter platform plugin_platform_interface]
- path_provider_windows 2.3.0 [ffi flutter path path_provider_platform_interface]
- permission_handler_android 13.0.1 [flutter permission_handler_platform_interface]
- permission_handler_apple 9.4.7 [flutter permission_handler_platform_interface]
- permission_handler_html 0.1.3+5 [flutter flutter_web_plugins permission_handler_platform_interface web]
- permission_handler_platform_interface 4.3.0 [flutter meta plugin_platform_interface]
- permission_handler_windows 0.2.1 [flutter permission_handler_platform_interface]
- petitparser 6.1.0 [meta collection]
- platform 3.1.6
- plugin_platform_interface 2.1.8 [meta]
- pool 1.5.1 [async stack_trace]
- posix 6.0.3 [ffi meta path]
- pub_semver 2.2.0 [collection]
- pubspec_parse 1.5.0 [checked_yaml collection json_annotation pub_semver yaml]
- qr 3.0.2 [meta]
- rfc_6901 0.2.0
- rive_common 0.4.15 [collection ffi flutter flutter_web_plugins graphs http meta plugin_platform_interface web]
- riverpod 2.6.1 [collection meta stack_trace state_notifier]
- riverpod_analyzer_utils 0.5.10 [analyzer collection crypto custom_lint_core freezed_annotation meta path source_span]
- rxdart 0.28.0
- shared_preferences_android 2.4.11 [flutter shared_preferences_platform_interface]
- shared_preferences_foundation 2.5.4 [flutter shared_preferences_platform_interface]
- shared_preferences_linux 2.4.1 [file flutter path path_provider_linux path_provider_platform_interface shared_preferences_platform_interface]
- shared_preferences_platform_interface 2.4.1 [flutter plugin_platform_interface]
- shared_preferences_web 2.4.3 [flutter flutter_web_plugins shared_preferences_platform_interface web]
- shared_preferences_windows 2.4.1 [file flutter path path_provider_platform_interface path_provider_windows shared_preferences_platform_interface]
- shelf 1.4.2 [async collection http_parser path stack_trace stream_channel]
- shelf_web_socket 3.0.0 [shelf stream_channel web_socket_channel]
- sky_engine 0.0.0
- source_gen 2.0.0 [analyzer async build dart_style glob path pub_semver source_span yaml]
- source_helper 1.3.7 [analyzer source_gen]
- source_span 1.10.1 [collection path term_glyph]
- sprintf 7.0.0
- sqflite 2.4.2 [flutter sqflite_android sqflite_darwin sqflite_platform_interface sqflite_common path]
- sqflite_android 2.4.2+1 [flutter sqflite_common path sqflite_platform_interface]
- sqflite_common 2.5.6 [synchronized path meta]
- sqflite_darwin 2.4.2 [flutter sqflite_platform_interface meta sqflite_common path]
- sqflite_platform_interface 2.4.0 [flutter platform sqflite_common plugin_platform_interface meta]
- stack_trace 1.12.1 [path]
- state_notifier 1.0.0 [meta]
- stream_channel 2.1.4 [async]
- stream_transform 2.1.1
- string_scanner 1.4.1 [source_span]
- syncfusion_flutter_core 31.1.21 [flutter vector_math]
- syncfusion_flutter_pdf 31.1.21 [flutter intl xml crypto convert http syncfusion_flutter_core]
- syncfusion_flutter_signaturepad 31.1.21 [flutter syncfusion_flutter_core]
- syncfusion_pdfviewer_linux 31.1.21 [flutter plugin_platform_interface]
- syncfusion_pdfviewer_macos 31.1.21 [flutter syncfusion_pdfviewer_platform_interface]
- syncfusion_pdfviewer_platform_interface 31.1.21 [flutter plugin_platform_interface]
- syncfusion_pdfviewer_web 31.1.21 [flutter flutter_web_plugins web syncfusion_pdfviewer_platform_interface]
- syncfusion_pdfviewer_windows 31.1.21 [flutter]
- synchronized 3.4.0
- term_glyph 1.2.2
- test_api 0.7.6 [async boolean_selector collection meta source_span stack_trace stream_channel string_scanner term_glyph]
- time 2.1.5 [clock]
- timezone 0.10.1 [http path]
- timing 1.0.2 [json_annotation]
- universal_html 2.2.4 [async csslib charcode collection html meta source_span typed_data universal_io]
- universal_io 2.2.2 [collection meta typed_data]
- url_launcher_android 6.3.17 [flutter url_launcher_platform_interface]
- url_launcher_ios 6.3.4 [flutter url_launcher_platform_interface]
- url_launcher_linux 3.2.1 [flutter url_launcher_platform_interface]
- url_launcher_macos 3.2.3 [flutter url_launcher_platform_interface]
- url_launcher_platform_interface 2.3.2 [flutter plugin_platform_interface]
- url_launcher_web 2.4.1 [flutter flutter_web_plugins url_launcher_platform_interface web]
- url_launcher_windows 3.1.4 [flutter url_launcher_platform_interface]
- vector_graphics 1.1.19 [flutter http vector_graphics_codec]
- vector_graphics_codec 1.1.13
- vector_graphics_compiler 1.1.18 [args meta path path_parsing vector_graphics_codec xml]
- vector_math 2.2.0
- vibration_platform_interface 0.1.0 [flutter plugin_platform_interface device_info_plus]
- vm_service 15.0.2
- watcher 1.1.2 [async path]
- web 1.1.1
- web_socket 1.0.1 [web]
- web_socket_channel 3.0.3 [async crypto stream_channel web web_socket]
- win32 5.14.0 [ffi]
- win32_registry 2.1.0 [ffi meta win32]
- xdg_directories 1.1.0 [meta path]
- xml 6.5.0 [collection meta petitparser]
- yaml 3.1.3 [collection source_span string_scanner]

Additional context and comments

No response

[SelaseKay]

Hi @LuigiFiorillo, could you provide a complete example app and detailed steps on reproducing this issue?

[LuigiFiorillo]

Hi @SelaseKay thank you for your reply!
I’ve prepared a full example to reproduce the issue and created a dedicated branch for it.

---

🧩 Branch and Setup

I created a new branch named issue-android-localization starting from the tag firebase_messaging-v16.0.0 in the official repository.
From there, I used the example app already included in the repo.

I then followed exactly the setup instructions provided in the example/lib/main.dart file.
As a result of running the commands indicated there, some files were automatically modified, including:

• android/app/google-services.json
• lib/firebase_options.dart

After that, I manually added my Firebase API key inside the scripts/ folder and inserted my device token in scripts/send-message.js.

---

🌍 Localization Setup

I added localized string resources for English and French under:

• android/app/src/main/res/values/strings.xml
• android/app/src/main/res/values-fr/strings.xml

Then I set my Android device language to French.

---

▶️ How to Reproduce

Launch the example app and keep it in background.
Use the modified scripts/send-message.js to send a message like the one below.

---

✅ Case 1 — Works correctly

{
    "token": "<DEVICE_TOKEN>",
    "data": {
        "foo": "bar"
    },
    "android": {
        "priority": "high",
        "notification": {
            "titleLocKey": "welcome_title",
            "titleLocArgs": ["Alice"],
            "bodyLocKey": "new_message_body",
            "bodyLocArgs": ["3", "Bob"]
        }
    },
    "apns": {
        "payload": {
            "aps": {
                "contentAvailable": true
            }
        }
    }
}

Result:
On Android, the notification is correctly localized according to the system language (for example, in French):
Bienvenue, Alice!
Vous avez 3 nouveau(x) message(s) de Bob.

---

❌ Case 2 — Unexpected behavior

If I modify the payload like this:

{
    "token": "<DEVICE_TOKEN>",
    "data": {
        "foo": "bar"
    },
    "android": {
        "priority": "high",
        "notification": {
            "title": "Default title",
            "titleLocKey": "welcome_title",
            "titleLocArgs": ["Alice"],
            "body": "Default body",
            "bodyLocKey": "new_message_body",
            "bodyLocArgs": ["3", "Bob"]
        }
    },
    "apns": {
        "payload": {
            "aps": {
                "contentAvailable": true
            }
        }
    }
}

On Android, the notification shows:
Default title
Default body

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⚙️ Expected Behavior

The expected behavior is that title and body should be used only if their corresponding localization keys (titleLocKey, bodyLocKey) are not found — this matches the behavior of the iOS SDK.

Currently, on Android, the SDK always prioritizes the static title and body fields when present, even if valid localization keys exist.