"走江湖卖假药" can be translated into English as "peddle fake medicines while wandering the江湖 (jianghu, referring to the world of itinerant performers, merchants, or adventurers in traditional Chinese culture)".
A more straightforward and commonly understood translation, without directly using "jianghu" (which might be culturally specific and not easily understood by all English speakers), could be:
"Wander around selling fake medicines" or "Itinerant vendor selling counterfeit drugs".The first option is more colloquial and captures the essence of "walking the江湖" (wandering around), while the second option is more formal and emphasizes the itinerant nature of the vendor along with the illegal activity of selling counterfeit drugs.