since the first large group of non-English Wikipedias came online.
Originally with spelled-out names rather than language codes, these
sites were:
chinese.wikipedia.com
esperanto.wikipedia.com
french.wikipedia.com
hebrew.wikipedia.com
italian.wikipedia.com
japanese.wikipedia.com
portuguese.wikipedia.com
spanish.wikipedia.com
russian.wikipedia.com
(from http://lists.wikimedia.org/
(deutsche and catalan had been created earlier that year)
The idea of having Wikipedias in multiple languages came from Jimbo in
March 2001 (http://lists.wikimedia.org/
note that the original German Wikipedia was actually set up at that
time, making it the second-oldest Wikipedia. Though the idea of using
two-letter domain codes was first raised then, after the above sites
were brought online in May there was further discussion, and the sites
were switched to two-letter codes a few days later:
http://lists.wikimedia.org/
Wikipedia Argentina also celebrated the es:wp10th anniversary today.
Happy tenth birthday, Wikipedias! (and many more!) May all of our
language editions flourish.