Is there a program that can convert a usb numpad press into a keyboard stroke? i.e. texting on an old phone - pre-hard/software keyboards. OS is raspbian.
You have to implement this either as an input method for the system if you need this to work for all apps, or implement this inside your app. Kodi does this by implementing this inside their own code, so it only works for them.
How to implement this, though, is a generic programming issue and if Google searches failed to satisfy you, would be better asked on Stack Overflow than here.