Oh, the number of times I've been asked that! Since I'm on my 3rd baby, the family knows better than to ask anymore. However, some of my past responses:
"I don't know." Then look at the baby "How long ARE you going to nurse?" When there is no response from baby/toddler...."He/She says he/she hasn't made up his/her mind yet." Then just shrug and smile.
"Well, technically we are in the process of weaning now. But like I said, it's a process. And that may take some time..... We'll let you know." (The definition of weaning is to introduce food to an exclusivilly breastfed baby.)
Of course reciting the recomendations from AAP, WHO, and Unicef always works.
When others come back and say "I only breasfed for ???? however long and my baby is healthy!" Just smile and say "Good for you! You seem confident in your choices!"
Mom to 6 year old (breastfed for 20 months)
4 year old (breastfed for 28 months)
16 month old (still nursing strong)