Sancho became the first player born this millennium to play for England when he came off the bench to replace Sterling and make his senior international debut in Friday's UEFA Nations League encounter in Croatia.
The call from England boss Gareth Southgate came after a sensational start to the Bundesliga season with Dortmund that has seen the 18-year-old register a league-high six assists and a goal in his first seven top-flight appearances of the season.
Watch: Jadon Sancho plays a pivotal role in Dortmund's Leverkusen comeback
Sterling trained alongside Sancho at City and praised the youngster for taking the bold decision to leave the English Premier League champions and move out of his comfort zone when he arrived in Germany in summer 2017.
"For someone so young to back themselves to go abroad is a credit to them. To go abroad so young and back yourself, that shows a lot about the person. He could have taken the easy route and stayed at City but he saw himself developing better," Sterling explained.
"That's what it's about in football — you have to judge your own situation and he did that perfectly and all credit to him. He has knuckled down in Germany and, when you're that age, it's probably something you need. To have that seclusion and be by yourself a bit and to concentrate solely on football. I'm really happy for him."
Sancho could get more international experience against Spain in Monday's Nations League game in Seville, and Sterling is convinced the rising BVB starlet has all the necessary ingredients to shine at the top of the game.
"He is a really good talent and someone I've thought highly of since the first time I saw him at Manchester City when he was training with us in pre-season," said the former Liverpool man.
"I thought highly of him - his work ethic and what he does with the ball. I know him really well and he's someone that is really modest but when he's on the field he wants to express his ability."