Yusufu Mieraili and Bilal Mohammed are accused of planting a bomb in a Hindu shrine in Bangkok's commercial heart in August 2015 that left 20 dead, mostly ethnic Chinese tourists.
The blast came weeks after Thailand's junta forcibly repatriated 109 Uighurs to China, where rights activists say the Muslim minority faces cultural and religious repression.
The timing prompted speculation that the attack was part of a revenge plot against a country that had been a key transit hub for Uighurs as Thailand's military leaders grew closer to Beijing.
Thai authorities have rejected that theory saying the attackers were part of a people-smuggling network angered by a recent crackdown, a motive most analysts say is simply not compelling.
The trial for the two men, who have been held in military prison for over a year, was delayed several times as the court struggled to find a suitable interpreter and rejected one provided by the defence.
People carry lighted candles near the Erawan Shrine at Rajprasong intersection for the victims an explosion in Bangkok, Thailand, Monday, Aug. 24, 2015. (AAP) Source: AP
The hearing finally started Tuesday after judges accepted two interpreters provided by the Chinese embassy and waved off objections from the defendants.
"I do not want translators from China because China does not respect Uighurs," Mohammed said through one of the interpreters.
"I want a translator who can speak Uighur from America, Canada, Australia or other countries," added Mieraili.
'Real concerns'
Uighurs, a Turkic minority, hail from China's westernmost province, Xinjiang.
The decision to use translators provided by the Chinese embassy is controversial because Uighurs have fled the region for years alleging they are the victims of state-sponsored persecution and assimilation policies that favour China's ethnic Han majority.
Beijing has also vowed to pursue Uighurs who flee abroad.
But a military judge on Tuesday rejected the defendants' concerns saying that the interpreters were "appropriate as they only do translation" and "speak the same language as the defendants".
Sam Zarifi, Asia director for the International Commission of Jurists (ICJ), which is monitoring the trial, said the appointments raised fresh doubts about the prospect of justice in a case being handled by an army tribunal.
"The current translators raise real concerns about the impartiality of the process," he told AFP, calling for the case to be moved to civilian court.
The first witness called by the prosecution on Tuesday was a police officer who was among the earliest to arrive on the scene after the bomb tore through the shrine, scattering debris and body parts.
"There were many deaths and injuries, both Thais and foreigners," police lieutenant colonel Somkiart Ploytabtim recalled.
Thailand's junta has been criticised for a murky investigation that appeared to wind down shortly after the arrest of the two men, leaving more than a dozen named suspects -- including alleged masterminds -- still at large.
Police and army officials also made confusing and often contradictory statements during the investigation.
The trial is expected to last until early 2018 with the court only sitting for a few days each month.
Prosecutors accuse Mohammed of placing the bomb inside a backpack at the shrine and say Mieraili was involved in transporting the device.
