Screenshots of Special:Preferences at thwiki and enwiki, showing that gadget tab at thwiki is lost.
At Thai Wikipedia, every gadget doesn't work at all. [[Special:Preferences#mw-prefsection-gadgets]] tab is also lost. This incident just happened today.
In addition, I also found that api has something wrong. I can't get registration time of any user who registered before December, 2005. I am very sure that it just happened today as well. Not sure if these are related or not.