If most of leather prducts come from china etc, Are we allowed to use them, keeping in mind the animal was not slaughtered according to islam.
The same can be asked about animal by products like Tallow which is used in alot of products (soaps, washing powder, womens makeup etc).
Jazakallah

Answer: only pigskin never gets paak, if an animal is slaughtered in the Islamic way, the skin becomes paak automatically, otherwise, if it is cleaned in a such way that no trace of najasat is left, the skin can be usable.
A word of caution for jackets which have pigskin, or iPhone holders made from pigskin, ur salah will not be valid with them on you, so be careful.