- Spanish (Mexican, Castellano, others?)
  - Chinese (Mandarin, Cantonese)
  - Hindi

These would be logical next steps with some important commonalities: broad base of native speakers, high importance in the US market (maybe less so for Hindi), and very important dialect differences. Mandarin, Cantonese, Hindi, and Russian could also force the issue of non-Romanized character sets.

Dutch... But I guess the odds are low for that, because the smaller user base. There are some companies focusing on care robotics emerging in the Netherlands though, which could use a service like this.

Japanese, due to demands for translation and robotics.