Taivoan language different from Siraya
Taivoan or Taivuan, is a Formosan language spoken until the end of the 19th century by the indigenous Taivoan people of Taiwan. Taivoan used to be regarded as a dialect of Siraya, but now more evidence has shown that they should be classified as separate languages. The corpora previously regarded as Siraya like the Gospel of St. Matthew and the Notes on Formulary of Christianity translated into "Siraya" by the Dutch people in the 17th century should be in Taivoan majorly.Since the January 2019 code release, SIL International has recognized Taivoan as an independent language and assigned the code tvx.Classification
The Taivoan language used to be regarded as a dialect of Siraya. However, more evidences have shown that it belongs to an independent language spoken by the Taivoan people.Documentary evidence
In "De Dagregisters van het Kasteel Zeelandia" written by the Dutch colonizers during 1629–1662, it was clearly said that when the Dutch people would like to speak to the chieftain of Cannacannavo (Kanakanavu), they needed to translate from Dutch to Sinckan (Siraya), from Sinckan to Tarroequan (possibly a Paiwan or a Rukai language), from Tarroequan to Taivoan, and from Taivoan to Cannacannavo."...... in Cannacannavo: Aloelavaos tot welcken de vertolckinge in Sinccans, Tarrocquans en Tevorangs geschiede, weder voor een jaer aengenomen" — "De Dagregisters van het Kasteel Zeelandia", pp.6–8Criticism against Candidius' famous assertion
Taivoan was considered by some scholars as a dialectal subgroup of the Siraya ever since George Candidius included "Tefurang" in the eight Siraya villages which he claimed all had "the same manners, customs and religion, and speak the same language." However,  American linguist Raleigh Ferrell reexaminates the Dutch materials and says "it appear that the Tevorangians were a distinct ethnolinguistic group, differing markedly in both language and culture from the Siraya." Ferrell mentions that, given that Candidius asserted that he was well familiar with the eight supposed Siraya villages including Tevorang, it's extremely doubtful that he ever actually visited the latter: "it is almost certain, in any case, that he had not visited Tevorang when he wrote his famous account in 1628. The first Dutch visit to Tevorang appears to have been in January 1636 [...]"Lee (2015) regards that, when Siraya was a lingua franca among at least eight indigenous communities in southwestern Taiwan plain, Taivoan people from Tevorangh, who has been proved to have their own language in "De Dagregisters van het Kasteel Zeelandia", might still need the translation service from Wanli, a neighbor community that shared common hunting field and also a militarily alliance with Tevorangh.Li noted in his "The Lingue Franche in Taiwan" that, Siraya exerted its influence over neighbouring languages in the southwestern plains in Taiwan, including Taivoan to the east and Makatao to the South in the 17th century, and became lingua franca in the whole area.Stress
It's hard to tell the actual stressing system of Taivoan in the 17th–19th century, as it's been a dormant language for nearly a hundred years. However, since nearly all the existing Taivoan words but the numerals pronounced by the elders fall on the final syllable, there has been a tendency to stress on the final syllable in modern Taivoan for language revitalization and education, compared to modern Siraya that the penultimate syllable is stressed.