From ce1f9ec96a13fe0ecaf35e060bea8d0f061cbf17 Mon Sep 17 00:00:00 2001
From: Dale Davies <dale.davies@catalyst-eu.net>
Date: Mon, 18 Sep 2023 13:37:57 +0100
Subject: [PATCH] MDL-79350 core: Do not store lang in session when readonly

---
 lib/moodlelib.php | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 7eec95072fe..86401d5ec78 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -10210,8 +10210,14 @@ function setup_lang_from_browser() {
         // Clean it properly for include.
         $lang = strtolower(clean_param($lang, PARAM_SAFEDIR));
         if (get_string_manager()->translation_exists($lang, false)) {
-            // Lang exists, set it in session.
-            $SESSION->lang = $lang;
+            // If the translation for this language exists then try to set it
+            // for the rest of the session, if this is a read only session then
+            // we can only set it temporarily in $CFG.
+            if (defined('READ_ONLY_SESSION') && !empty($CFG->enable_read_only_sessions)) {
+                $CFG->lang = $lang;
+            } else {
+                $SESSION->lang = $lang;
+            }
             // We have finished. Go out.
             break;
         }