I figure the top Scottish clubs are shopping for players in the same places as Championship clubs in England. So I'd recommend two Swedish players for you:
- Kristoffer Olsson of FC Midtjylland in Denmark, for the M/AM(C) creative positions
- Oscar Lewicki of Malmo FF, for the DM/M(C) ball-winning positions
I imagine both would be affordable and happy to join Glasgow Rangers; they're both potential captains and I think they both already speak English, but check them in-game to make sure. They both have Wikipedia pages (from which I learn that in their youth, Olsson was at Arsenal and Lewicki was with Bayern Munich) if you want some real world background on them:
https://en.wikipedia.org/wiki/Kristoffer_Olsson
https://en.wikipedia.org/wiki/Oscar_Lewicki
In my journeyman FM16 save, I took Lewicki to Everton (got sacked when 1st in table due to boardroom takeover), Olsson to Sheffield Wednesday (promoted as runners-up) and then both of them to AFC Bournemouth (promoted via play-offs); the fact that I signed and re-signed them shows that I was happy with their performances and at Bournemouth they were my Captain and Vice-Captain for a while.
Other players who perform well at Championship level - and, I'm thinking therefore in the Scottish Premiership - include Zach Clough (Bolton Wanderers, False-9), Callum Slattery (Southampton U18s, Deep-Lying Playmaker) and - if you can get them on-loan - Patrick Roberts (Manchester City, AM(L)/IF(R)) and Julian Brandt (Bayer Leverkusen, AM(R)/IF(L)).