Baring work with actual linguistics the "next best actually practically useful work with language(s)" discipline is law.-
Language (and keen, precise language at that) is the ultimate tool of a jurist - and internationally, there's much good that can be done in that field by someone with such language talents.-
Now, given the quality (and quantity) of the gifts involved, and a penchant for language, I of course humbly also second "computational linguistics" - given how he seems to enjoy depth in the analysis (and, comparative analysis at that) of language structure.-