MDL-22015 core_string_manager cache can be disabled by setting $CFG->disablelangdiskcache

config-dist.php

@@ -371,6 +371,9 @@ $CFG->admin = 'admin';
 // Prevent theme caching
 // $CFG->themerev = -1; // NOT FOR PRODUCTION SERVERS!
 //
+// Prevent core_string_manager on-disk cache
+// $CFG->disablelangdiskcache = true; // NOT FOR PRODUCTION SERVERS!
+//
 // When working with production data on test servers, no emails should ever be send to real users
 // $CFG->noemailever = true;    // NOT FOR PRODUCTION SERVERS!
 //

lib/moodlelib.php

@@ -5934,7 +5934,7 @@ class core_string_manager implements string_manager {
         }
 
         // try on-disk cache then
-        if (file_exists($this->cacheroot . "/$lang/$component")) {
+        if (empty($CFG->disablelangdiskcache) and file_exists($this->cacheroot . "/$lang/$component")) {
             $this->countdiskcache++;
             eval('$this->cache[$lang][$component] = ' . file_get_contents($this->cacheroot . "/$lang/$component") . ';');
             return $this->cache[$lang][$component];
@@ -6015,8 +6015,10 @@ class core_string_manager implements string_manager {
         // now we have a list of strings from all possible sources. put it into both in-memory and on-disk
         // caches so we do not need to do all this merging and dependecies resolving again
         $this->cache[$lang][$component] = $string;
-        check_dir_exists($this->cacheroot . '/' . $lang, true, true);
-        file_put_contents($this->cacheroot . "/$lang/$component", var_export($string, true));
+        if (empty($CFG->disablelangdiskcache)) {
+            check_dir_exists($this->cacheroot . '/' . $lang, true, true);
+            file_put_contents($this->cacheroot . "/$lang/$component", var_export($string, true));
+        }
         return $string;
     }