I understand you want to change the wording of your sale bubbles on your products. This should be accessible through your theme language editor in your admin. You can find this by going to Online Store > Themes > Click the “Actions” drop down menu > Choose Language Editor.
On my test store I searched for the word “Sale”, this brings up all uses of the word in my store’s front end. I can now edit the language, save and check to see if this applies the change I want to the online store experience. Go ahead and try this!