Mitochondrial tRNA methyltransferase that mediates methylation of cytosine to 5-methylcytosine (m5C at position 34 of mt-tRNA(Met. mt-tRNA(Met methylation at cytosine(34 takes place at the wobble position of the anticodon and initiates the formation of 5-formylcytosine (f(5c at this position. mt-tRNA(Met containing the f(5c modification at the wobble position enables recognition of the AUA codon in addition to the AUG codon, expanding codon recognition in mitochondrial translation.