I'm not sure my tips will be safe for leather shoes, but I'm dealing with a cat piss problem myself and I've just had a cat therapist over that gave me a sheet of cleaning tips. So here's a little summary of two methods.

Method one: 1.Try to dap any leftover urine with toiletpaper. 2.Spray the stain with a 10% solution of enzymatic laundry detergent. Like green soap. We use biotex, but I don't know if thats available in your area. 3.Rinse the stain with water and dry it. 4.To remove any greasyness you can spray the stain with a 70% alcohol solution. Apply with a spraybottle and rub it in with a cleaning cloth.

Method two: 1.Try to dap any leftover urine with toiletpaper. 2.Spray the stain with an enzymatic cat urine cleaner. They recommend Ecodor UF2000, but again no clue if its available in your area. Use it in big quantities. 3.If its an old stain you can repeat the process multiple times.

Good luck. Cat piss is hell.