We're also a bilingual household. My husband and I however split the languages, if you can call it that. I only speak to my daughter in English & he only does in Afrikaans. Our families are also divided that way. She started saying her first basic words at 10 months. By 12 months she had a vocab of about 8-10 words. She is now 15 months and is saying 2 word phrases, albeit only a few of them. Her vocab has increased significantly. The majority of her words are English. I'm thinking it's because I'm around her the most of the time. She does however understand what my husband & family says when speaking Afrikaans. In your case I would recommend you speak to your pediatrician at the next check up to see if this is in the normal range or not. Try not to be too concerned about it, until you've got some more facts.