Earlier quoted context omitted.
The European Commission has just announced an agreement whereby English will be the official language of the European Union rather than German, which was the other possibility. As part of the negotiations, the British Government conceded that English spelling had some room for improvement and has accepted a 5- year phase-in plan that would become known as "Euro-English". In the first year, "s" will replace the soft "…
This spelling reform was pioneered by Mark Twain[1]. [1] http://www.i18nguy.com/twain.html
(Edit 2: the Economist came later! see downthread)
Edit: the joke originated as a letter to the Economist in 1971: https://web.archive.org/web/20200807181810/https://lettersof.... The classic internet version (referencing the European Commission) was a later rewrite—no idea by whom. It's interesting that the original was a UK in-joke ("Haweve, sins xe Wely, xe Airiy, and xe Skots du not spik Ingliy") but the rewrite became more outward-facing, a sort of Euroskeptic joke when light humor about that was still possible (I got it in an email in the 90s), as well as quite a bit funnier.
Misassigning it to Mark Twain is not surprising, because all great quotes by obscure people get reattributed to famous writers over time. Also, Twain wrote a famous and funny essay complaining about German (https://faculty.georgetown.edu/jod/texts/twain.german.html), and he was interested in alphabet reform too (http://www.online-literature.com/twain/1322/).