Mr Saadallah will appear at Westminster Magistrates' Court on Monday.
Police forensic officers work near the scene of a fatal multiple stabbing attack in Forbury Gardens, central Reading, England.
Saadallah, who moved to the United Kingdom as a refugee in 2012, is alleged to have turned towards one group of friends sitting on the grass, stabbing four of them, before turning to another group of five friends sitting nearby, stabbing two of them, one in the back and one in the cheek.
Neil Basu, the national head of Counter Terrorism Policing, said that as the coronavirus lockdown was beginning to ease, members of the public should play their part in protecting themselves and others from what he called the scourge of terrorism. We need all the prayers for Joe and the Ritchie and Bennett families'.
And scientist Mr Wails was described as "always happy" and a person who "always made people smile".
A further three people were taken to hospital for treatment for their injuries and have since been released from hospital.
People pay their respects to the murdered schoolteacher James Furlong outside The Holt School
It began at 19:00 BST, marking a week since the attack.
Relatives of the victims and members of the local community lit candles, while the UK's Interior Minister Priti Patel also attended the vigil, lighting a candle and paying her respects.
Police declared the stabbings as a terrorist incident the day after the attack, but they have not said what they think the motive was and noted the investigating is ongoing.
While the speeches were televised, residents of Reading were encouraged not to gather in large numbers due to social distancing measures, but to light candles on their doorsteps. Two other men who were sitting with friends nearby were also stabbed, one in the back while the other suffered a cut to his cheek.
Chief Constable of Thames Valley Police, John Campbell added: "A week on from the tragic incident in Reading, Thames Valley Police is proud to be coming together in solidarity with the community to remember the three innocent men, David, James and Joseph, who lost their lives".
"I know it will take time for everyone to heal but we stand alongside you and will do all that we can to support you, as your Police".