Some initial machinery for lattices over number fields appear in Magma in V2.22. In particular, automorphism group and isometries can be computed for totally positive definite lattices (over totally real fields). This work is inspired by code of Gael Collinet, and in the future will be subsumed into his project to implement functionality for Lorentz lattices.
The category of number field lattices is LatNF, and the elements of such lattices are LatNFElt, with these being user-defined types.