Localize notification emails

Add support for translating notification emails and send localized
notifications, based on the user's language preferences. Also, update
the translations Makefile to add strings from the notification script
to the message catalog.

Implements FS#31850.

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

aurweb/l10n.py

@@ -0,0 +1,16 @@
+import gettext
+
+
+class Translator:
+    def __init__(self):
+        self._translator = {}
+
+    def translate(self, s, lang):
+        if lang == 'en':
+            return s
+        if lang not in self._translator:
+            self._translator[lang] = gettext.translation("aur",
+                                                         "../../web/locale",
+                                                         languages=[lang])
+        self._translator[lang].install()
+        return _(s)