Add i18n support for French and German with browser language detection

auth.py

@@ -12,6 +12,7 @@ from models import (
     get_all_households,
     count_household_users,
 )
+from i18n import t
 
 auth_bp = Blueprint("auth", __name__)
 
@@ -23,12 +24,12 @@ def login():
         password = request.form.get("password", "")
 
         if not username or not password:
-            flash("Username and password are required.", "error")
+            flash(t("Username and password are required."), "error")
             return render_template("login.html")
 
         user = get_user_by_username(username)
         if user is None or not check_password_hash(user["password_hash"], password):
-            flash("Invalid username or password.", "error")
+            flash(t("Invalid username or password."), "error")
             return render_template("login.html")
 
         household_id = user["household_id"]
@@ -59,32 +60,32 @@ def register():
 
         errors = []
         if not username or len(username) < 2:
-            errors.append("Username must be at least 2 characters.")
+            errors.append(t("Username must be at least 2 characters."))
         if not password or len(password) < 4:
-            errors.append("Password must be at least 4 characters.")
+            errors.append(t("Password must be at least 4 characters."))
         if password != confirm:
-            errors.append("Passwords do not match.")
+            errors.append(t("Passwords do not match."))
         if get_user_by_username(username):
-            errors.append("Username already taken.")
+            errors.append(t("Username already taken."))
 
         target_household_id = None
 
         if household_action == "create":
             if not new_household_name:
-                errors.append("Household name is required.")
+                errors.append(t("Household name is required."))
             elif get_household_by_name(new_household_name):
-                errors.append("A household with that name already exists.")
+                errors.append(t("A household with that name already exists."))
             else:
                 household = create_household(new_household_name)
                 target_household_id = household["id"]
                 is_admin = True  # First user in a new household is admin
         else:
             if not household_id:
-                errors.append("Please select a household.")
+                errors.append(t("Please select a household."))
             else:
                 hh = get_household_by_id(int(household_id))
                 if hh is None:
-                    errors.append("Selected household does not exist.")
+                    errors.append(t("Selected household does not exist."))
                 else:
                     target_household_id = hh["id"]
                     is_admin = False
@@ -104,7 +105,7 @@ def register():
         session["household_id"] = user["household_id"]
         session["household_name"] = get_household_by_id(target_household_id)["name"]
 
-        flash("Account created! Welcome to your household.", "success")
+        flash(t("Account created! Welcome to your household."), "success")
         return redirect(url_for("meals.dashboard"))
 
     return render_template("register.html", households=households)