This list is very useful for translators as it optimises their effort in the early stages of translating the interface: they will have the most benefit if they translate these messages from top to bottom.
Measured on Tuesday 13 November 2007 from 10:43 CET to 12:56 CET. Data has been gathered out of 1 of every 50 pages served from an application server of the Wikimedia Foundation, with profiling rules designed by Tim Starling and Domas and was retrieved with this URL. In this timeframe, the 5000 most often used messages have been called on application servers 23,530,127 times. Messages which do not belong to the core messages have been filtered out. Optional messages and EXIF messages have also been filtered out.
At the bottom of the list are messages that are not that often used, but important for a proper look and feel for all users: create account, sign on, page history, delete page, move page, protect page, watchlist.
On 19 December 2008 from 23:16 CET to 20 December 2008 00:44 CET another measurement was done, giving about 9.7M samples. In this case it was no longer possible to have one output for all Wikimedia wikis. Instead, there was output for the English language Wikipedia (en), the German language Wikipedia (de), and all other wikis (others)*. All 5000 or fewer hits** got a descending rating (5000 for the most often used message). For all 3 results, the counts were added, and from that a new list of about 500 most often used messages in the MediaWiki core was compiled.
On 14 May 2011 a measurement was made, following the same method as the previous measurements. A list of about 500 messages from MediaWiki core was selected, and messages in the the form to sign up that were not yet part of the list were manually added.