The nmodl language is used to define new cell mechanisms (eg ionic currents) for the NEURON simulator. This project outlines some possible pipelines for expressing models defined using mod in NeuroML2/LEMS.
The pynmodl repositry contains a (python-based) parser for mod files, providing infrastructure for building compilers from mod to other languages. It includes basic support for generating LEMS (usage example).
See http://www.opensourcebrain.org/docs#Converting_To_NeuroML2