Several additional details are needed to determine the cause of your 6/12 vision. It may well be due to the traumatic cataract or may be due to other causes - for example corneal scar or astigmatism, if there was corneal injury.
Your eye evaluation consists of 2 important steps. The first step is to determine whether it is the cataract that is to blame for 6/12 vision. The second step is to determine whether there is potential for vision to improve to better than 6/12. For the first step you will need a manifest refraction and, probably, a diagnostic hard contact lens refraction. If vision improves with these tests then you DO NOT need cataract surgery as the cause of your vision of 6/12 is not cataract. However, if vision does not improve then the second step test needs to be done, that is - to determine if there is a potential for vision improvement. A Potential Acuity Meter (PAM) test or a Near Vision illuminated pin-hole test may be performed. If vision improves then there is potential benefit in removing the cataract, however, if vision does not improve cataract removal will not help as the retina may have been damaged. You will then need careful retinal evaluation. You should also ask yourself why you want the cataract surgery in the first place. A 6/12 vision in not bad and if the other eye has 6/6 vision then you probably have no vision difficulty when you use both eyes together. However, if you feel that your daily routine activities are being affected by the 6/12 vision, then you may consider surgery. The risks of cataract surgery after trauma are higher than a normal cataract surgery operation. You will have to discuss these with your physician. You do not have to go for cataract surgery simply because a cataract is present. That is the wrong reason. If 6/12 bothers you visually and glasses or contact lens does not improve it, then considering cataract surgery is reasonable.