The fact is there is no such thing as rule of law without lots of institutions and individuals (private and public) taking responsibility for arbitrating truth. And there's no freedom of speech without allowing them to do it.
Someone could murder someone, but due to lack of evidence they are found “not guilty”. But that’s not the same as “the truth is this person did not commit murder”. It’s simply a finding that the state didn’t prove its case.
A formal process of examining evidence marshaled in the service of arguments supporting/refuting a claim sounds practically equivalent to most forms of determining truth. Because it is.
Not only that, but there are segments of the law where truth is explicitly invoked, ie "truth is an absolute defense against defamation."