Specifically dimethylates a single guanine residue at position 27 of tRNA(Tyr) using S-adenosyl-L-methionine as donor of the methyl groups (PubMed:39786990, PubMed:39786998). Dimethylation at position 27 of tRNA(Tyr) is required for efficient translation of tyrosine codons (PubMed:39786990, PubMed:39786998). Also required to maintain 3-(3-amino-3-carboxypropyl)uridine (acp3U) in the D-loop of several cytoplasmic tRNAs (PubMed:39786990, PubMed:39786998). . This is the function of TRMT1L (tRNA methyltransferase 1L, ENSG00000121486).