apt: request translation when executing the mirror check

By setting the LANG variable and passing clean_locale=False, the apt-get
command will be translated if the locale definition exists on the
system.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquity/server/apt.py

@@ -173,7 +173,10 @@ class AptConfigurer:
             apt_cmd.append(
                     f"-o{target}::DefaultEnabled=false")
 
-        proc = await astart_command(apt_cmd, stderr=subprocess.STDOUT)
+        env = os.environ.copy()
+        env["LANG"] = self.app.base_model.locale.selected_language
+        proc = await astart_command(apt_cmd, stderr=subprocess.STDOUT,
+                                    clean_locale=False, env=env)
 
         async def _reader():
             while not proc.stdout.at_eof():

subiquity/server/tests/test_apt.py

@@ -60,6 +60,7 @@ class TestAptConfigurer(SubiTestCase):
         self.model = Mock()
         self.model.mirror = MirrorModel()
         self.model.proxy = ProxyModel()
+        self.model.locale.selected_language = "en_US.UTF-8"
         self.app = make_app(self.model)
         self.configurer = AptConfigurer(self.app, AsyncMock(), '')