La domanda è intrigante, lo ammetterete. E Microsoft ha pubblicato tre pubblicità ai loro prodotti in altrettante lingue inesistenti.
Un articolo che tratta diffusamente l’argomento è questo qui: languagelog.ldc.upenn.edu/nll/?p=4626
Native speakers of Mandarin, Cantonese, Japanese, and Korean declare that it is not any of those languages. The first time I listened to them, the ads sounded as though they contained elements of some Wu topolect, a bit like mangled Shanghainese, but I could also definitely hear bits of Mandarin, albeit with unusual tonal contours and slurring. What was most perplexing of all to me was that, although I was certain that the ads contained Chinese phrases and sentences, every Chinese person to whom I showed them emphatically maintained that they could not understand a single word! In contrast, several non-native speakers of Mandarin said they could pick out a word of Chinese here and there.
A couple of people from China suggested to me that the language might be that of Ruian (near Wenzhou) 瑞安的温州话, which has about 5,000,000 speakers. But I only think they said that because the speech of Ruian is famous for being virtually impossible for outsiders to comprehend in the slightest, so much so that (along with other Wenzhou topolects) it has supposedly been used in wartime as a secret language (e.g., when the Chinese fought against the Vietnamese in 1979).