Downgrade missing translations from error to debug

This is something the developer of a module is supposed to deal with. If you are just using SSP, it doesn't make much sense to have your log files flooded by errors about missing translation files or directories, since you cannot do anything about it and the original english text will be used anyway.

lib/SimpleSAML/Locale/Localization.php

@@ -240,7 +240,7 @@ class Localization
             $langPath = $this->getLangPath($domain);
         } catch (\Exception $e) {
             $error = "Something went wrong when trying to get path to language file, cannot load domain '$domain'.";
-            Logger::error($_SERVER['PHP_SELF'].' - '.$error);
+            Logger::debug($_SERVER['PHP_SELF'].' - '.$error);
             if ($catchException) {
                 // bail out!
                 return;
@@ -255,7 +255,7 @@ class Localization
             $this->translator->loadTranslations($translations);
         } else {
             $error = "Localization file '$poFile' not found in '$langPath', falling back to default";
-            Logger::error($_SERVER['PHP_SELF'].' - '.$error);
+            Logger::debug($_SERVER['PHP_SELF'].' - '.$error);
         }
     }