Can we eat kosher meat? Also, i have heard from a few Islamic teachers that we can eat meat from Christian Orthodox countries like KFC in Poland. Is this true?
Anything certified kosher is automatically halal except alcohol. Kosher certification for slaughterhouses requires the presence of a person from a Jewish religious institution who oversees the slaughter to make sure it is carried out according to Jewish religious law, which is compatible with Islamic law.
We are technically allowed to eat food from Christians, provided that there are no other issues with the food. We cannot eat pork even if it is from a Christian country, since pork is forbidden regardless of its source. In the same way, animals that are dead at the time of slaughter are impermissible to eat regardless of the source, and since a significant portion of the meat and poultry coming from Western non-kosher slaughterhouses is from dead animals/birds (as much as 10%, as was discovered by the European Fatwa Council), we cannot eat it. The meat you buy from a supermarket and the meat in a typical burger chain’s offerings could be from an animal or bird that was dead before slaughter for all that you know, for this reason Muslims have to avoid it.
If you know Christians who slaughter their animals and birds properly and allow the blood to leave the carcass, you are allowed to eat the meat they sell. But if it is slaughterhouse meat, or if it is from Christian farmers who do not bleed the carcass, or who perform the slaughter in other ways not compatible with Islamic law, you are not allowed to eat it.
In general, Christians have no religious standards regarding slaughter, therefore one should consider meat provided by them automatically haram unless one knows the source well and knows that they conduct the slaughter and bleeding properly. As for meat from Jewish kosher-certified sources, one can automatically assume it is halal since the slaughtering involves the presence of a religious representative.