There are two possible answers, depending on your intention:
- If you want to know the expectable current, Alex' calculation is pretty reasonable. You can make it even more exact by considering the third REXT = open point, and get 2.2 mA and an nearly perfect linear relation.
- If you want to read a guaranteed maximum current from the datasheet, e.g. for a power supply dimensioning, all calculations and estimations are void. The only validated assumption is, that the current will be below the specified maximum current for REXT = 470R.