Why does Christopher dislike strangers? To what does he compare strangers?

Christopher doesn't like strangers because he doesn't like people he has never met before. He compares strangers to the people he met while vacationing in France, who spoke a foreign language.

"I do not like strangers because I do not like people I have never met before. They are hard to understand. It is like being in France, which is where we went on holiday sometimes when mother was alive, to camp."

How is Christopher different from the other kids at his school?

From the book the curious incident of the dog in the night-time