feat: store the lang in session

so it is not forgot after OAuth2 redirections

Author: azmeuk

src/auth_playground/i18n.py

@@ -1,4 +1,5 @@
 from flask import g
+from flask import session
 from flask_babel import Babel
 from flask_babel import get_locale
 from werkzeug.exceptions import NotFound
@@ -42,7 +43,9 @@ def add_language_code(endpoint, values):
             return
 
         if not g.get("lang_code"):
-            g.lang_code = app.config.get("BABEL_DEFAULT_LOCALE", "en")
+            g.lang_code = session.get(
+                "lang_code", app.config.get("BABEL_DEFAULT_LOCALE", "en")
+            )
 
         if "lang_code" not in values:
             values.setdefault("lang_code", g.lang_code)
@@ -52,6 +55,7 @@ def pull_lang_code(endpoint, values):
         """Extract language code from URL and store in g.lang_code for i18n routes."""
         if values is not None and "lang_code" in values:
             g.lang_code = values.pop("lang_code")
+            session["lang_code"] = g.lang_code
 
     @app.before_request
     def before_request():

src/auth_playground/translations/messages.pot

@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PROJECT VERSION\n"
 "Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
-"POT-Creation-Date: 2026-01-16 15:33+0100\n"
+"POT-Creation-Date: 2026-01-16 16:03+0100\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"