FAA Validation of Foreign Certificate
A straight FAA validation of a foreign PPL is quite easy and requires some paperwork and a meeting at a US FAA FSDO. This results in an FAA Private Pilot certificate ‘issued on the basis of a foreign certificate’ (regardless of whether the foreign certificate has higher ratings). This certificate requires the foreign Pilots License to be maintained as valid. Instructions are here:
Adding Ratings and joining our Accelerated Course
If the holder of the Foreign Pilot License has an Instrument Rating it is possible to add Instrument Privileges to the FAA Certificate based on a Foreign Certificate by completing an FAA Instrument Knowledge Test. However, this does not qualify for Instrument Privileges towards a US Commercial Pilot Certificate. If the intention is to take a US Commercial Checkride to have a Certificate NOT based on a foreign certificate (required for ratings like Commercial, CFI, etc), then a US Instrument Rating needs to be added to the FAA Private Certificate based on a Foreign Certificate by taking an FAA Instrument Knowledge Test AND FAA Checkride for the Instrument Rating. Then, you can begin to prepare for the Commercial Rating. For this you need to meet the experience requirements (log flight training in the areas required) and study/prepare for and take the the FAA Commercial Knowledge Test and Practical (oral/flight) Test with an FAA examiner or Designated Pilot Examiner. Luckily, most/all of your logged foreign time counts towards the Commercial requirements.
Sling Pilot Academy can help you through this process, which would look like this:
A Foreign Pilot who obtains an FAA Private Pilot Certificate based on a Foreign Pilot Certificate and has at least 80 hours of total time would be well-suited to join our 6-month Accelerated Program ("from Private").