There is a report that ULS throws a syntax error in IE 8: https://de.wikipedia.org/wiki/Wikipedia:Fragen_zur_Wikipedia#.22Benachrichtigungen.22-Button_funktioniert_nicht_mehr
The offending line comes from jquery.i18n.language.js, at the very end:
$.extend( $.i18n.languages, { default: language } );
Obviously, IE 8 doesn't like the keyword default as unquoted object key. Upstream caused by https://github.com/wikimedia/jquery.i18n/commit/71c4219e72ac7754ec0c1ba8cc1814a1367a1057, ULS-extension by https://git.wikimedia.org/commitdiff/mediawiki%2Fextensions%2FUniversalLanguageSelector.git/05dd11fcb07e8851bb69739839a8cf748aaa6fef