Aww, jangan risau sangat lagi, at one year old memang ada yang slow talker, especially kalau bapak dia quiet type pun memang boleh jadi! Yang bagus tu dia paham instruction dan respond, tu sign dia mentally okay je, cuma memang "heavy mouth" macam you cakap. A few of my mum friends ada anak macam tu jugak, around 18-20 months baru start meletus words, pastu cakap non-stop lah pulak! Tapi sebab you slightly worried, worth having a quick chat with your pediatrician just untuk peace of mind, depa boleh assess properly and rule out anything, then you can relax. Meantime, keep talking to him, read books together, engage dia, yang tu semua help je!