What is the ruling on eating chicken imported from Christian countries where electrical stunning is used in its slaughter, and is it obligatory to ascertain the source of chicken when being hosted, and is it necessary to wash one's foot if it touches chicken remnants discarded in the street?

Avoiding imported chicken is good, but one is not obligated to ask the host about the origin of the chicken. As long as the host is Muslim, the default assumption is that it is permissible. As for chicken found in the streets, it is not ruled impure or carrion merely based on doubt, for the default state of things is purity. If you are certain that it is carrion and it is difficult to avoid, then there is no harm in taking the concession in such a situation.