Stand your ground, this was about safety, the job they hired you to do. I would make sure that, if it's NOT in company policy/hiring, that it gets there in writing ASAP. Would not matter if it were Spanish, or Farsi, or Hebrew, it's about SAFETY.
You are in a lose-lose situation if your company doesn't back you. If there was an accident because of poor communications because you turned the other cheek and let them speak in a language not designated, you can dang well bet someone would sue you and the company over it.