The following topic came up in a Spanish class I am auditing: To what degree do the KCS and the KCS de Mexico run as a combined system, and to what degree is the combined system "bilingual?"
I would assume that KCSM would use the native language of whatever territory its operating in. Mexican crews do not operate in the US, American crews do not operate in Mexico. Two different railroads.
Why not contact the company with regards to your question of language (notice their site is be-lingual): http://www.kcsouthern.com/