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/utils.py

@@ -13,13 +13,13 @@ from django.utils import timezone
 from django.utils.timesince import timesince
 from django.utils.translation import gettext as _
 from django.utils.translation import pgettext
-from django.utils.translation import gettext_lazy
+from django.utils.translation import gettext_noop
 from libvirt import libvirtError
 
 from accounts.models import UserInstance
 from appsettings.models import AppSettings
 from instances.models import Instance
-from vrtManager.util import ConnectionFailed
+from vrtManager.util import ConnectionFailed, OperationError
 
 from . import jobs
 
@@ -49,7 +49,7 @@ TRANSPORT_ERROR_CODES = {
     libvirt.VIR_ERR_SSH,
     libvirt.VIR_ERR_LIBSSH,
 }
-UNREACHABLE = gettext_lazy("The host of this virtual machine cannot be reached right now.")
+UNREACHABLE = gettext_noop("The host of this virtual machine cannot be reached right now.")
 
 BOUNDS = {"WORKER_CONCURRENCY": (1, 16, 4), "JOB_RETENTION_DAYS": (1, 3650, 30)}
 
@@ -61,7 +61,29 @@ def safe_text(text):
     return text
 
 
-def public_error_text(exception):
+# A text a job keeps for later (its error, its result's warning) is a list of
+# messages, each our English text, marked with gettext_noop, and its values:
+# words() puts them in the language of whoever reads them. A text that is not
+# ours (libvirt's) is a message without values and stays as it is.
+def say(text, **values):
+    return [{"text": safe_text(text), "values": {key: safe_text(value) for key, value in values.items()}}]
+
+
+def said(exception):
+    """The messages of an exception: an OperationError's text and values, else its text."""
+    if isinstance(exception, OperationError):
+        return say(exception.text, **exception.values)
+    return say(exception)
+
+
+def words(messages):
+    """messages in the active language, each a sentence of its own."""
+    parts = [_(m["text"]) % m["values"] if m["values"] else _(m["text"]) for m in messages]
+    return " ".join(part if last or part.endswith((".", "。", "!", "?")) else part + "."
+                    for last, part in ((i == len(parts) - 1, part) for i, part in enumerate(parts)))
+
+
+def public_error(exception):
     """The error for users who do not see the hosts: a connection error names
     the host and how it is reached, so they learn only that it cannot be reached."""
     connection_error = isinstance(exception, ConnectionFailed) or (
@@ -69,7 +91,11 @@ def public_error_text(exception):
         and exception.get_error_domain() in TRANSPORT_ERROR_DOMAINS
         and exception.get_error_code() in TRANSPORT_ERROR_CODES
     )
-    return str(UNREACHABLE) if connection_error else str(exception)
+    return say(UNREACHABLE) if connection_error else said(exception)
+
+
+def public_error_text(exception):
+    return words(public_error(exception))
 
 
 def check_params(params):