The 60-year-old, who co-founded the Viasna human rights group, is one of the most prominent of hundreds of Belarusians who were jailed during a violent crackdown on anti-government protests that erupted in the summer of 2020.
Byalyatski, who shared the Nobel Peace Prize with Russian rights group Memorial and Ukraine's Center for Civil Liberties in October, was arrested in 2021 along with two co-workers from Viasna.
The trio face from seven to 12 years in jail on charges of financing protests and smuggling money. Byalyatski has not commented on the allegations publicly and his lawyer is prohibited from disclosing information about the case.
A fourth rights defender who fled Belarus is being prosecuted in absentia in the same case.
Viasna said on Twitter that the judge had refused to conduct the trial in Belarusian instead of Russian, and rejected Byalyatski's request for a translator.
The group took a leading role in providing legal and financial assistance to hundreds of Belarusians who were jailed during mass protests that flared when long-time leader Alexander Lukashenko, in power since 1994, claimed a landslide election victory in 2020.
"The allegations against our colleagues are linked to their human rights activity, the Viasna human rights centre's provision of help to the victims of politically motivated persecution," the group said of the case.
Byalyatski and his colleagues have been labelled "political prisoners" by fellow rights defenders. Those rights advocates estimate there are around 1,500 political prisoners in Belarusian prisons.
Around 50,000 people have been detained for taking part in protests or criticising the authorities since 2020, they say.
(Reporting by Tom Balmforth and Dan Peleschuk, Editing by Timothy Heritage)
