Notwithstanding their attempt to argue for the historical Protestant view of justification, one Protestant scholar wrote that, even in legal/forensic contexts, the LXX’s use of δικαιοω is not merely declarative:
In the Greek version of the OT, the cognate verb dikaioō did not imply a legal fiction, but recognizing one as righteous, including in forensic contexts (cf. Gen 44:16; Isa 43:9, 26; Ezek 44:24): judges must not “acquit the guilty” (Exod 23:7), but must “justify,” i.e., pronounce righteous, the innocent (Deut 25:1). God himself would punish the guilty but “justify” and vindicate the righteous (1 Kgs 8:32; 2 Chr 6:23); he himself was “justified,” or “shown to be right,” when he pronounced just judgment, even against the psalmist (Ps 51:4, in Rom 3:4). (Craig S. Keener, Romans [Eugene, Oreg.: Cascade Books, 2009], 28)
