A Unity 3D app should be fairly straightforwards in terms of creating a navigable interface with associated spatially located sound. I am not sure about what times of sound output would be possible from such an app for installation purposes by it would suffice for a mobile experience.
The archive will have wiki pages for each sound file and many of those created will have GPS coordinates associated with it easily obtainable from the json file of the wiki page.
It should also be possible to embed this information in the appropriate sound file format as part of the archiving process when this is not already present (for instance for sound files uploaded by Telegram).
I am unsure of audio input in Unity 3D, but should be straight forwards.
An alternative would be to use an open source C++ library and embed that in a Livecode application. An advantage of this approach might be the ability to create solutions which work in low resource situation of the Raspberry Pi.
It would be good to strategise the creation of the mobile app with a flexible and extensible software environment for physical installations. This may point to using libraries in a C++ environment over using Unity 3D.
However Unity 3D would be a great way to start with a working prototype, and has the advantage of easy integration with rich visual environments and game-like interfaces on mobile.