It's not the only one missing if I can trust "svn diff"... But those are not necessary in English. Missing string equals empty string.
That string is from one of my patches Dandello was supposed to merge in.
--- C:/Users/Mika/AppData/Local/Temp/Main.lng-revBASE.svn000.tmp.lng Mon Jul 07 20:11:16 2014
+++ C:/build/yabb/trunk/cgi-bin/yabb2/Languages/English/Main.lng Sat Jul 19 01:18:41 2014
@@ -18,6 +18,7 @@
@days = ('Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday');
@months = ('Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec');
+@months_m = ('Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec');
@days_short = ('Sun','Mon','Tue','Wed','Thu','Fri','Sat'); # for smtp
%maintxt = (
@@ -46,6 +47,7 @@
'28' => 'Guest',
'30' => 'on',
'30a' => 'wrote on',
+'30b' => '',
'31' => 'Quote',
'32' => 'Go',
'34' => 'Login',
@@ -129,6 +131,8 @@
'758' => 'Moved',
'769' => 'Today',
'769a'=> 'Yesterday',
+'770' => '', #month suffix for January 1.
+'770a' => '', #month suffix for 1. January
'773' => 'Would you like to print this page now?',
'900b' => 'Back',
'900s' => 'Submit',