Hi @jill,
With Cesium for Unreal you can access two different coordinate systems, Geographic (Longitude, Latitude, Height, which is EPSG:4979) and ECEF(x, y, z, EPSG:4978).
The Unreal world coordinate system doesn’t follow any global coordinate system, but you can convert between UE coordinates, EPSG:4979, and EPSG:4978 with the methods found on CesiumGeoreference. If you’re trying to load a shapefile, you’d probably want to transform the coordinates of the shapefile to EPSG:4979, then convert them to UE coordinates for placement.
This tool may also be of use.
-Alex