diff --git a/docs/admin/backup.rst b/docs/admin/backup.rst
index 955719237f32..23f099db5fde 100644
--- a/docs/admin/backup.rst
+++ b/docs/admin/backup.rst
@@ -32,6 +32,14 @@ The generated backups are kept on the server as configured by
 :setting:`PROJECT_BACKUP_KEEP_DAYS` and :setting:`PROJECT_BACKUP_KEEP_COUNT`
 (it defaults to keep at most 3 backups for 30 days).
 
+.. note::
+
+   Restoring of the backup might fail if the restoring server has different set
+   of :ref:`languages` or different configuration of
+   :setting:`SIMPLIFY_LANGUAGES`. The restore will tell you which language
+   codes could not be processed and you can then add missing langage
+   definitions manually.
+
 Automated backup using BorgBackup
 ---------------------------------
 
diff --git a/weblate/trans/backups.py b/weblate/trans/backups.py
index c1d67835969b..65702c30691f 100644
--- a/weblate/trans/backups.py
+++ b/weblate/trans/backups.py
@@ -8,6 +8,7 @@
 
 import json
 import os
+from collections import defaultdict
 from datetime import datetime
 from itertools import chain
 from shutil import copyfileobj
@@ -329,6 +330,18 @@ def load_components(self, zipfile, callback: Callable | None = None):
                     raise ValueError(
                         f'Component {data["component"]["name"]} uses unsupported VCS: {data["component"]["vcs"]}'
                     )
+                # Validate translations have unique languages
+                languages = defaultdict(list)
+                for item in data["translations"]:
+                    language = self.import_language(item["language_code"])
+                    languages[language.code].append(item["language_code"])
+
+                for code, values in languages.items():
+                    if len(values) > 1:
+                        raise ValueError(
+                            f"Several languages from backup map to single language on this server {values} -> {code}"
+                        )
+
                 if callback is not None:
                     callback(zipfile, data)
 
diff --git a/weblate/trans/tests/data/projectbackup-duplicate.zip b/weblate/trans/tests/data/projectbackup-duplicate.zip
new file mode 100644
index 000000000000..48ca21544d4a
Binary files /dev/null and b/weblate/trans/tests/data/projectbackup-duplicate.zip differ
diff --git a/weblate/trans/tests/test_backups.py b/weblate/trans/tests/test_backups.py
index 7c3910dad36f..5df032202366 100644
--- a/weblate/trans/tests/test_backups.py
+++ b/weblate/trans/tests/test_backups.py
@@ -23,6 +23,7 @@
 
 TEST_SCREENSHOT = get_test_file("screenshot.png")
 TEST_BACKUP = get_test_file("projectbackup-4.14.zip")
+TEST_BACKUP_DUPLICATE = get_test_file("projectbackup-duplicate.zip")
 
 
 class BackupsTest(ViewTestCase):
@@ -154,6 +155,13 @@ def test_restore_4_14(self):
             set(restored.label_set.values_list("name", "color")),
         )
 
+    def test_restore_duplicate(self):
+        if not connection.features.can_return_rows_from_bulk_insert:
+            raise SkipTest("Not supported")
+        restore = ProjectBackup(TEST_BACKUP_DUPLICATE)
+        with self.assertRaises(ValueError):
+            restore.validate()
+
     def test_cleanup(self):
         cleanup_project_backups()
         self.assertLessEqual(len(self.project.list_backups()), 3)