Mr Salwai is being tried on corruption, bribery and perjury charges.
This comes after Mr Kalsakau had made a criminal complaint, contesting Mr Salwai's assertion that his appointment of parliamentary secretaries in 2016 was approved by his cabinet.
As the first witness in the Supreme Court trial in Port Vila, on Wednesday, Mr Kalsakau repeated that claim.
On Thursday he told the court that parliamentary secretaries had, in fact, been introduced in 2007 by the Sato Kilman government, of which Mr Kalsakau was a member.
The prosecution had orginally planned to call 29 witnesses but indications now are that fewer will appear.
Mr Kalsakau, who was opposition leader in 2016, believes Mr Salwai used the parliamentary secretary positions to beef up his numbers in the parliament, to stave off a vote of no confidence.