The 18-year-old is set to start for his country when they open their Group A campaign against reigning champions Bangladesh in the West Indies on Sunday afternoon.
Sales starred in England' s warm-up victory over Papua New Guinea in midweek, claiming three for 14 and also hitting a quickfire 46 not out from just 31 balls as his team claimed a thumping 281-run win.
That performance, allied with some decent showings in the one-day series in Sri Lanka in November, should go a long way to ensuring the former Overstone Park youngster gets the nod when coach Richard Dawson names his team for Sunday's tournament opener.
And that would top off a remarkable few months for Sales, who only made his first team debut for the Steelbacks in the Royal London One Day Cup in August, before going on to make his Championship debut later in the summer.
That led to him being offered and signing a three-year professional contract at Wantage Road, as well as his selection for the Under-19 World Cup, where England will be based in St Kitts & Nevis.
Asked about his selection for the World Cup, Sadler said: "It is fantastic, and Salesy's rise has been quite quick hasn't it?
"He was playing some academy and second team cricket, he put in some performances and he matured, and then obviously the opportunity to play in the first team came along and he took it with both hands.
"He was brilliant in the 50-over competition for us, he did well in the four-day stuff, and his recognition with England Under-19s is fantastic and we are delighted for him."
Sales, the son of former Northants skipper and batsman David, seems to have taken his recent rise in his stride, and Sadler admits he has been impressed.
"I can't speak highly enough of Salesy, he has been great," said the 40-year-old, who took over as head coach from David Ripley in October.
"He is very, very raw, he has some fantastic potential, but we don't want to pile too much pressure on him at the minute, we just want him playing his cricket, enjoying it, and learning along the way.
"We will support him all the way, but it is brilliant for the cricket club that he is involved in the England set-up."
Asked about what Sales has to offer as a player, Sadler added: "I see him as an all-rounder.
"I am not going to pigeon-hole him into anything, but he is a modern day cricketer.
"He can bat, he can bowl, and he can field as he is a natural athlete.
"With that, we don't want to pile too much pressure on him, we just want him playing, learning, contributing, whether it's with England Under-19s or the first or second team at Northampton.
"Wherever he is, he just has to turn up, learn and we will support him.
"But he is somebody who can contribute in all three disciplines, which is exciting."
After England's opener against Bangladesh on Sunday, they play Canada next Tuesday (Jan 18) and then wrap up Group A with a clash with the United Arab Emirates on Thursday (Jan 20).
The top two from the group will qualify for the Super League stage of the competition, with the bottom two going into the Plate competition.