I reached out Dr. Yuan-chao Tung, who is the director of the Center for Indigenous Studies at National Taiwan University in order to help find someone who can verify the language for the Sakizaya Wikipedia . He referred me to an Austronesian languages expert who basically said that it would be difficult to find an independent expert because all of the scholars who are experts in Sakizaya are already contributors to it! That's more than good enough of a verification for me. :-)
Their activity  has been steady for a long time, with plenty of contributors. The localization  is done for the most used messages (they have actually translated around 6,000 MediaWiki messages – 10 times what's required! MediaWiki core is 74 % finished, and several extensions are translated as well). Note that their language code, [szy], is very new – it was approved in January of this year. Before that, they used the language code [ais], which has now been deprecated in ISO 639. It's a long story. Until today  the language code [ais] was still used for Sakizaya in MediaWiki, but me and Nikerabbit (I did the easy parts, Nikerabbit the hard parts) changed it to the correct [szy].
Something to celebrate about this is that it will be the first Wikipedia in an indigenous language of Taiwan. Taiwan is considered the birthplace of the Austronesian language family, and it is there that the variety of Austronesian languages is greatest – out the primary branches of Austronesian languages, all but one (the Malayo-Polynesian languages) are spoken exclusively in Taiwan. So this will be a nice extension of Wikimedia's language diversity.
Another interesting thing about this language is that it doesn't seem to use capital letters at the start of sentences, but only in proper nouns. This will be the second language Wikipedia (after Lojban) to need to have the $wgCapitalLinks setting set to 'false'. :-)