My tongue and mouth are numb- could this be mouth cancer?

Kinda sounds like you may have something like swelling blocking the blood supply to the nerve and or the whole area. I would go to a dental er and see if they can give you an explanation. Also if traveling maybe try some anti inflammatory meds tylenol etc. Dental swelling can take months to years to totally resolve. I have heard the dental clinics in Brazil and SA are VERY reasonable for the cash payer. Check it out. Good Luck.