Christian people are least likely to speak which language

The correct answer is - Arabic.

The Christian people, in general, would not speak the Arabic language. There's multiple reasons for that, but the biggest ones are the religion, and the historical disputes between the Christians and the Muslims that dominate the Arab countries.

Because of the intolerance between the two, the Christians do not find the Arabic language as attractive for studying, nor do they migrate towards the countries where the language is spoken, so they don't have the need for it.