When can i start running again after a severe ankle injury (fracture/dislocation)?

It depends: By "severe" i assume you required surgery and have a little hardware store in there. After the initial 2 month period of non-weight bearing and another 2 months of physical therapy, you may begin power walks at 6 months, and resume your running on a limited basis in 8 months. If your injury was not that severe and you didn't have surgery, you'd probably be running again in 4-5 months.

Ankle dislocation: After surgery for ankle fracture dislocation (with or without open fracture), it usually takes about 2-3 months for the bone fractures to heal if properly aligned. The ankle joint may have damage as well and may take longer to heal due swelling or other possible complications, however if everything is perfect, typically another 2-3 months of therapy before returning to light running at 5-6 months.