diff --git a/lib/GaletteOAuth2/Authorization/UserHelper.php b/lib/GaletteOAuth2/Authorization/UserHelper.php
index 89096bf..e5c5616 100644
--- a/lib/GaletteOAuth2/Authorization/UserHelper.php
+++ b/lib/GaletteOAuth2/Authorization/UserHelper.php
@@ -14,10 +14,12 @@
 use DI\Attribute\Inject;
 use Galette\Core\Db;
 use Galette\Core\History;
+use Galette\Core\I18n;
 use Galette\Core\Login;
 use Galette\Core\Preferences;
 use Galette\Entity\Adherent;
 use Galette\Entity\Social;
+use Galette\Entity\Status;
 use GaletteOAuth2\Tools\Config;
 use GaletteOAuth2\Tools\Debug;
 use RKA\Session;
@@ -40,6 +42,7 @@ public function __construct(
         private readonly Login $login,
         private readonly History $history,
         private readonly Preferences $preferences,
+        private readonly I18n $i18n,
         private readonly Messages $flash,
         #[Inject('oauth_session')]
         private readonly Session $session
@@ -129,6 +132,34 @@ public function getUserData(int $id, string $acl, array $scopes, bool $legacy =
             throw new UserAuthorizationException(_T('User not found.', 'oauth2'));
         }
 
+        //data are sent to client applications, that do not share member's session
+        $current_lang = $this->i18n->getID();
+        if ($member->language && $member->language !== $current_lang) {
+            $this->i18n->changeLanguage($member->language);
+        }
+        try {
+            return $this->buildUserData($member, $acl, $scopes, $legacy);
+        } finally {
+            if ($this->i18n->getID() !== $current_lang) {
+                $this->i18n->changeLanguage($current_lang);
+            }
+        }
+    }
+
+    /**
+     * Build user data, in current language
+     *
+     * @param Adherent $member Member
+     * @param string   $acl    Requested authorization
+     * @param string[] $scopes Scopes
+     * @param bool     $legacy Legacy mode for data
+     *
+     * @return array<string, mixed>
+     * @throws UserAuthorizationException
+     * @throws \Throwable
+     */
+    private function buildUserData(Adherent $member, string $acl, array $scopes, bool $legacy): array
+    {
         //check active member? Covers $acl === self::AUTH_ACTIVE
         if (!$member->isActive()) {
             throw new UserAuthorizationException(_T("Sorry, you can't login because you are not an active member.", "oauth2"));
@@ -209,7 +240,8 @@ public function getUserData(int $id, string $acl, array $scopes, bool $legacy =
 
         //member:personal
         if (in_array('member:personal', $scopes)) {
-            $oauth_data['birthdate'] = $member->birthdate;
+            //raw value: formatted dates follow current language
+            $oauth_data['birthdate'] = $member->rbirthdate;
             $oauth_data['birthplace'] = $member->birth_place;
             $oauth_data['job'] = $member->job;
             $oauth_data['gender'] = $member->sgender;
@@ -272,12 +304,12 @@ public function getUserData(int $id, string $acl, array $scopes, bool $legacy =
 
         //member:groups
         if (in_array('member:groups', $scopes)) {
-            $oauth_data['groups'] = self::getUserGroups($member, $legacy);
+            $oauth_data['groups'] = $this->getUserGroups($member, $legacy);
         }
 
         //member:due_date
         if (in_array('member:due_date', $scopes)) {
-            $oauth_data['due_date'] = $member->due_date;
+            $oauth_data['due_date'] = $member->rdue_date;
         }
 
         return $oauth_data;
@@ -291,7 +323,7 @@ public function getUserData(int $id, string $acl, array $scopes, bool $legacy =
      *
      * @return string[]
      */
-    protected static function getUserGroups(Adherent $member, bool $legacy = false): array
+    private function getUserGroups(Adherent $member, bool $legacy = false): array
     {
         $groups = array_map(
             function ($group) {
@@ -300,7 +332,9 @@ function ($group) {
             array_values($member->getGroups())
         );
 
-        $groups[] = $member->sstatus;
+        //untranslated: groups are mapped by client applications, they must not depend on language
+        $status = new Status($this->zdb);
+        $groups[] = (string)$status->getLabel($member->status, false);
 
         if ($member->isAdmin()) {
             $groups[] = 'admin';
diff --git a/tests/GaletteOAuth2/Authorization/tests/units/UserHelper.php b/tests/GaletteOAuth2/Authorization/tests/units/UserHelper.php
index 770d453..9cb3a7d 100644
--- a/tests/GaletteOAuth2/Authorization/tests/units/UserHelper.php
+++ b/tests/GaletteOAuth2/Authorization/tests/units/UserHelper.php
@@ -128,7 +128,7 @@ public function testGetUserData(): void
 
         $this->assertSame(
             $expected_base + [
-                'birthdate' => $user_data['birthdate'],
+                'birthdate' => $this->dataAdherentOne()['ddn_adh'],
                 'birthplace' => 'Gonzalez-sur-Meunier',
                 'job' => 'Chef de fabrication',
                 'gender' => 'Unspecified',
@@ -277,6 +277,95 @@ public function testGetUserData(): void
         );
     }
 
+    /**
+     * Store a member speaking french
+     *
+     * @return \Galette\Entity\Adherent
+     */
+    private function getFrenchMember(): \Galette\Entity\Adherent
+    {
+        $this->logSuperAdmin();
+        $adh = new \Galette\Entity\Adherent($this->zdb);
+        $adh->setDependencies(
+            $this->preferences,
+            $this->members_fields,
+            $this->history
+        );
+
+        $data = $this->dataAdherentOne();
+        $data['pref_lang'] = 'fr_FR';
+        $data['sexe_adh'] = \Galette\Entity\Adherent::WOMAN;
+        $check = $adh->check($data, [], []);
+        if (is_array($check)) {
+            var_dump($check);
+        }
+        $this->assertTrue($check);
+
+        $this->assertTrue($adh->store());
+        $this->login->logout();
+
+        return $adh;
+    }
+
+    /**
+     * Test user data are translated in member's language, whatever the current one is
+     *
+     * @return void
+     */
+    public function testGetUserDataInMemberLanguage(): void
+    {
+        $member = $this->getFrenchMember();
+        $data = $this->dataAdherentOne();
+        $this->assertSame('en_US', $this->i18n->getID());
+
+        $user_data = $this->container->get(\GaletteOAuth2\Authorization\UserHelper::class)->getUserData(
+            $member->id,
+            '',
+            ['member', 'member:personal', 'member:groups', 'member:due_date']
+        );
+
+        $this->assertSame('fr_FR', $user_data['locale']);
+        $this->assertSame('Femme', $user_data['gender']);
+        //dates are not localized
+        $this->assertSame($data['ddn_adh'], $user_data['birthdate']);
+        $this->assertNull($user_data['due_date']);
+        //status in groups is not translated: client applications rely on it
+        $this->assertSame(['Non-member'], $user_data['groups']);
+
+        //current language is restored
+        $this->assertSame('en_US', $this->i18n->getID());
+        $this->assertSame('Woman', _T('Woman'));
+    }
+
+    /**
+     * Test refusal messages are in member's language, and current language is restored
+     *
+     * @return void
+     */
+    public function testRefusalInMemberLanguage(): void
+    {
+        $member = $this->getFrenchMember();
+
+        $this->i18n->changeLanguage('fr_FR');
+        $expected = _T("Sorry, you can't login because you are not a team member.", 'oauth2');
+        $this->i18n->changeLanguage('en_US');
+        $this->assertNotSame("Sorry, you can't login because you are not a team member.", $expected);
+
+        $exception_thrown = false;
+        try {
+            $this->container->get(\GaletteOAuth2\Authorization\UserHelper::class)->getUserData(
+                $member->id,
+                \GaletteOAuth2\Authorization\UserHelper::AUTH_TEAMONLY,
+                ['member']
+            );
+        } catch (\GaletteOAuth2\Authorization\UserAuthorizationException $e) {
+            $exception_thrown = true;
+            $this->assertSame($expected, $e->getMessage());
+        }
+        $this->assertTrue($exception_thrown);
+        $this->assertSame('en_US', $this->i18n->getID());
+    }
+
     /**
      * Test requireAdmin
      *
diff --git a/tests/GaletteOAuth2/Controllers/tests/units/AuthorizationCodeFlow.php b/tests/GaletteOAuth2/Controllers/tests/units/AuthorizationCodeFlow.php
index 3bc59ad..54a6b61 100644
--- a/tests/GaletteOAuth2/Controllers/tests/units/AuthorizationCodeFlow.php
+++ b/tests/GaletteOAuth2/Controllers/tests/units/AuthorizationCodeFlow.php
@@ -263,6 +263,46 @@ public function testUserData(): void
         $this->assertArrayHasKey('due_date', $user);
     }
 
+    /**
+     * Test user data are sent in member's language, not in the one of client's request
+     *
+     * @return void
+     */
+    public function testUserDataInMemberLanguage(): void
+    {
+        $this->logSuperAdmin();
+        $member = clone $this->getMemberOne();
+        $check = $member->check(
+            [
+                'bool_admin_adh' => '1',
+                'pref_lang' => 'fr_FR',
+                'sexe_adh' => \Galette\Entity\Adherent::MAN,
+            ],
+            [],
+            []
+        );
+        if (is_array($check)) {
+            var_dump($check);
+        }
+        $this->assertTrue($check);
+        $this->assertTrue($member->store());
+        $this->login->logout();
+
+        $tokens = $this->exchangeCode(
+            $this->getAuthorizationCode($member->id, ['member', 'member:personal', 'member:groups'])
+        );
+        $this->assertSame('en_US', $this->i18n->getID());
+        $test_response = $this->requestUser($tokens['access_token']);
+        $this->assertSame(200, $test_response->getStatusCode());
+        $user = json_decode((string)$test_response->getBody(), true);
+
+        $this->assertSame('fr_FR', $user['locale']);
+        $this->assertSame('Homme', $user['gender']);
+        $this->assertSame($this->dataAdherentOne()['ddn_adh'], $user['birthdate']);
+        $this->assertSame(['Non-member', 'admin'], $user['groups']);
+        $this->assertSame('en_US', $this->i18n->getID());
+    }
+
     /**
      * Test user data are refused when member is no longer authorized
      *