Update Babel package

Upgrade the Babel package to version ^2.12 in response to the Python
version upgrade. Fixes #483.

ambuda/__init__.py

@@ -8,14 +8,14 @@
 import logging
 import sys
 
+import config
 import sentry_sdk
 from dotenv import load_dotenv
 from flask import Flask, session
 from flask_babel import Babel, pgettext
 from sentry_sdk.integrations.flask import FlaskIntegration
 from sqlalchemy import exc
 
-import config
 from ambuda import admin as admin_manager
 from ambuda import auth as auth_manager
 from ambuda import checks, filters, queries
@@ -111,13 +111,13 @@ def create_app(config_env: str):
     # Database
     _initialize_db_session(app, config_env)
 
-    # Extensions
-    babel = Babel(app)
-
-    @babel.localeselector
+    # A custom Babel locale_selector.
     def get_locale():
         return session.get("locale", config_spec.BABEL_DEFAULT_LOCALE)
 
+    # Extensions
+    Babel(app, locale_selector=get_locale)
+
     login_manager = auth_manager.create_login_manager()
     login_manager.init_app(app)