fix(i18n): define get_locale function before passing to Babel constructor

- Flask-Babel 4.0.0 requires locale_selector function to be defined first
- Move function definition before Babel initialization
- All tests still pass

app.py

@@ -13,9 +13,6 @@ from flask_babel import Babel, gettext, lazy_gettext
 app = Flask(__name__)
 app.secret_key = 'your_secret_key_here'
 
-# Babel configuration
-babel = Babel(app)
-
 # Configure supported languages
 app.config['BABEL_DEFAULT_LOCALE'] = 'es'
 app.config['LANGUAGES'] = {
@@ -26,7 +23,7 @@ app.config['LANGUAGES'] = {
 # Configure translation directory
 app.config['BABEL_TRANSLATION_DIRECTORIES'] = 'translations'
 
-@babel.locale_selector
+# Locale selector function
 def get_locale():
     # Try to get language from URL parameter
     lang = request.args.get('lang')
@@ -38,6 +35,9 @@ def get_locale():
     # Try to get from browser preferences
     return request.accept_languages.best_match(app.config['LANGUAGES'].keys())
 
+# Initialize Babel with locale selector
+babel = Babel(app, locale_selector=get_locale)
+
 # Context processor to make language and config available in templates
 @app.context_processor
 def inject_global_variables():