Defender Langmead returned to the bench for the 1-0 first-leg win after being sidelined since the end of March with a knee injury.
Striker Platt (calf) had missed the previous three games before also being named among the substitutes on Thursday night and both players will be hoping to feature.
Winger Ishmel Demontagnac lasted 76 minutes in the first leg after returning from a hamstring injury and will be monitored, while leading goalscorer Adebayo Akinfenwa and winger Chris Hackett played key roles for the Cobblers having been rested in recent matches.
Manager Aidy Boothroyd has no major new problems as his side look to defend a slender one-goal advantage.
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- Adebayo Akinfenwa