feat(operations): a job's error and warning show in the reader's language

A job stored its error and its result's warning as English text, much
of it built with the values in it (volume paths, a disk, libvirt's
error), so no catalog could translate it, and the job pages and panel
showed English whatever the language.

A job now stores them as messages: our English text, marked for
translation, and its values; libvirt's own text is a message without
values and is shown as it is. The jobs API and pages put them in the
reader's language. OperationError keeps its text and values apart for
the same reason, so a refusal raised while a job is submitted is shown
translated too. Messages one after another still read as sentences.

Errors stored before are kept as one message each, shown as they were.

operations/tests/test_api.py

@@ -12,6 +12,7 @@ from instances.models import Instance
 from operations import claims, jobs
 from operations.models import Claim, Operation
 from operations.tests import fakes
+from operations.utils import say
 
 
 class OperationsApiTestCase(TransactionTestCase):
@@ -35,6 +36,17 @@ class OperationsApiTestCase(TransactionTestCase):
         Operation.objects.filter(pk=self.op.pk).update(time_limit=60, started_at=timezone.now() - timedelta(seconds=61))
         self.assertEqual(self.client.get(url).json()["phase"], "Merging the snapshot (over its time limit)")
 
+    def test_the_error_and_warning_come_in_the_users_language_with_their_values(self):
+        # ours with its values; libvirt's text as it is
+        Operation.objects.filter(pk=self.op.pk).update(
+            state=Operation.FAILED,
+            error=say("The pool has no volume named %(name)s", name="disk.qcow2") + say("unable to open: busy"),
+            result={"warning": say("The copy was not made")})
+        self.client.force_login(self.owner)
+        job = self.client.get(f"/api/v1/operations/{self.op.pk}/", HTTP_ACCEPT_LANGUAGE="tr").json()
+        self.assertEqual(job["error"], "Havuzda disk.qcow2 adında birim yok. unable to open: busy")
+        self.assertEqual(job["result"]["warning"], "Kopya oluşturulmadı")
+
     def test_users_list_only_their_own_jobs(self):
         self.client.force_login(self.other)
         self.assertEqual(self.client.get("/api/v1/operations/").json()["count"], 0)