stiff ankles. border to my sls work :(

as the title says, i have very poor mobility to my ankles, so that every time i try to squat or do a variation for my sls work, i tend to lift the back of my foot and stand on the front, and then i lose my balance AND my knees get in front of my toes. this may have happened due to bad walking and running habit(i run with the front of my foot). i think that being a tae kwon do athlete for 5-6 years 8-14 y.o.(we have to hop on our front side of the foot) made my calves stiff and non mobile. Sorry for my english. Does anyone know what i could do to overcome this problem?

You could try to do squats with the back of your foot raised by a object and eventually reduce the height, you could try assisted squats by grabbing something in front of you and then executing a proper squat, Another way can be try to squat lower form workout to workout without raising your ankle and holding a weight with your hands for counterbalance.  

Assume the bottom of the deck squat with your back to a wall. Spending time in the bottom position will improve your ankle mobility.

...and strech them calves

i will take into consideration all of your info and i will post the results when there is any improvement thank you very much!

Calf stretch off a step will help you.

Calf step off a step is probably the first order of business

If you are capable of a comfortable full squat position you can try this stretch;

From kneeling on the floor with feet flexed and toes tucked under, sit up straight and slightly back until you are able to transition to a full squat without falling or rolling. Start wide and work narrow, watch your shins a little to begin with too

i tried placing my heel to a 5kg plate so that my heel is elevated. i did 3x30s each foot calf stretch at the beginning and the end of the workout. Now my static sls feel more comfortable

Agree on calf stretch. Vary the calf stretch by doing it on the ground, doing it off a step, straight leg, bent leg. These variations will target different areas with the bent knee versions targeting the ankle and Achilles more directly. Also consider adding weight (weighted vest is ideal for me personally - but don't go with too much weight to begin).

Mix in some contract relax with some bouncing or pulsing in the various positions.

Hi, here's a video of an athlete working on his tight ankles over at Mobility WOD: http://www.mobilitywod.com/2012/02/case-study-tight-ankles-bad-squatting/ I did this and have had some success, but it's been a very gradual process. (Would doubtless have better if I were more religious about the stretching.) My right ankle is almost there, my left is still a ways off. 

This might be part of your problem. My understanding is that the prohibition on knees in front of toes is mostly mythical. Since the argument for it originally was excess load on the knees while supporting heavy weight on the back, there is even less reason to pay attention to it when doing a bodyweight squat. 

It does work somewhat as a cue to make sure you are sitting back into the squat instead of just folding at the knees, but it shouldn't be a guide to proper form in my opinion. That is, the focus should be on hinging at the hip and getting full depth with your body mostly upright. If you think about your knees, the more important cue is to keep them tracked inline with the feet and to resist collapsing inside of the toes towards the midline.

Of course, this is mostly theoretical for me since I also have ankle and hip mobility issues that keep me from a good full depth squat. For ankle mobility, I'm using 1) integrated mobility from F1, 2) calf stretches (the bent leg versions in particular), 3) sitting for time in a squat position. Slow going, but am seeing improvements.