whenever you feel need to self talk just do that inside your head and not out loud. this way other people would think you are just fine and as other has mentioned try to reduce/stop it
I used to have a feeling that, when I self-talked, I could not help but actually murmuring with my mouth, speaking out actually, especially when I was relatively more anxious, although my voice was not very loud when I spoke out. Then I decided that overly frequent self-talk was not very helpful for me