[FIX] base: remove duplicated translation before update

Since 160d6577, the translations must be unique on the source.
When calling insert_missing on a field, the final step is to set the correct
source on every translation to keep them synchronised.

In case the translation looked like:

  id   | lang  | src | type  | res_id |       name
---------+-------+-----+-------+--------+------------------
    42 | fr_FR | KGM | model |      2 | product.uom,name
    43 | fr_FR | kg  | model |      2 | product.uom,name

The final step will fail as violating the unicity constraint.

Remove duplicated translations before making the update.
It was chosen to keep the latest translation as it should be the most up to
date (e.g. after an import creating duplicated translations).

Add a non-regression test for previous change

opw-1864123
Closes #25787

odoo/addons/base/models/ir_translation.py

@@ -616,6 +616,14 @@ class IrTranslation(models.Model):
                             SELECT 1 FROM ir_translation
                             WHERE lang=l.code AND type='model' AND name=%(name)s AND res_id=%(res_id)s
                         );
+
+                        DELETE FROM ir_translation dup
+                        WHERE type='model' AND name=%(name)s AND res_id=%(res_id)s
+                            AND dup.id NOT IN (SELECT MAX(t.id)
+                                       FROM ir_translation t
+                                       WHERE t.lang=dup.lang AND type='model' AND name=%(name)s AND res_id=%(res_id)s
+                            );
+
                         UPDATE ir_translation SET src=%(src)s
                         WHERE type='model' AND name=%(name)s AND res_id=%(res_id)s;
                     """

odoo/addons/base/tests/test_translate.py

@@ -275,6 +275,37 @@ class TestTranslation(TransactionCase):
         self.assertEqual(categories.ids, [padawans.id, self.customers.id],
             "Search ordered by translated name should return Padawans (Apprentis) before Customers (Clients)")
 
+    def test_105_duplicated_translation(self):
+        """ Test synchronizing translations with duplicated source """
+        # create a category with a French translation
+        padawans = self.env['res.partner.category'].create({'name': 'Padawan'})
+        self.env['ir.translation'].create({
+            'type': 'model',
+            'name': 'res.partner.category,name',
+            'module':'base',
+            'lang': 'fr_FR',
+            'res_id': padawans.id,
+            'value': 'Apprenti',
+            'state': 'translated',
+        })
+        # change name and insert a duplicate manually
+        padawans.write({'name': 'Padawans'})
+        self.env['ir.translation'].create({
+            'type': 'model',
+            'name': 'res.partner.category,name',
+            'module':'base',
+            'lang': 'fr_FR',
+            'res_id': padawans.id,
+            'value': 'Apprentis',
+            'state': 'translated',
+        })
+        self.env['ir.translation'].translate_fields('res.partner.category', padawans.id, 'name')
+        translations = self.env['ir.translation'].search([
+            ('res_id', '=', padawans.id), ('name', '=', 'res.partner.category,name')
+        ])
+        self.assertEqual(len(translations), 1, "Translations were not merged after `translate_fields` call")
+        self.assertEqual(translations.value, "Apprentis", "The most recent translation must stay")
+
 
 class TestXMLTranslation(TransactionCase):
     def setUp(self):