Catalyzes the NADPH-dependent synthesis of dihydrouridine, a modified base found in the D-loop of most tRNAs (PubMed:15994936, PubMed:26429968, PubMed:30149704, PubMed:34798057, PubMed:38680565). Specifically modifies U20 in cytoplasmic tRNAs (PubMed:38680565). Activity depends on the presence of guanosine at position 19 in the tRNA substrate (PubMed:38680565). Negatively regulates the activation of EIF2AK2/PKR (PubMed:18096616). {ECO:0000269|PubMed:15994936, ECO:0000269|PubMed:18096616, ECO:0000269|PubMed:26429968, ECO:0000269|PubMed:30149704, ECO:0000269|PubMed:34798057, ECO:0000269|PubMed:38680565}. This is the function of DUS2 (dihydrouridine synthase 2, ENSG00000167264).