--- b/searx/locales.py
+++ a/searx/locales.py
@@ -86,7 +86,7 @@
         use_translation = flask.request.form.get('use-translation')
         if use_translation in ADDITIONAL_TRANSLATIONS:
             babel_ext = flask_babel.current_app.extensions['babel']
+            return Translations.load(next(babel_ext.translation_directories), use_translation)
-            return Translations.load(babel_ext.translation_directories[0], use_translation)
     return _flask_babel_get_translations()
 
 
--- b/searx/webapp.py
+++ a/searx/webapp.py
@@ -160,6 +160,8 @@
 app.jinja_env.filters['group_engines_in_tab'] = group_engines_in_tab  # pylint: disable=no-member
 app.secret_key = settings['server']['secret_key']
 
+babel = Babel(app)
+
 timeout_text = gettext('timeout')
 parsing_error_text = gettext('parsing error')
 http_protocol_error_text = gettext('HTTP protocol error')
@@ -209,15 +211,13 @@
 request = typing.cast(ExtendedRequest, flask.request)
 
 
+@babel.localeselector
 def get_locale():
     locale = localeselector()
     logger.debug("%s uses locale `%s`", urllib.parse.quote(request.url), locale)
     return locale
 
 
-babel = Babel(app, locale_selector=get_locale)
-
-
 def _get_browser_language(req, lang_list):
     for lang in req.headers.get("Accept-Language", "en").split(","):
         if ';' in lang: