The Latam website is a nightmare, but it recently got updated - so for the first time, I was able to select seats online for our flights booked as a Delta Codeshare by the travel agency for our guided Peru Tour in September. However, the payment never went through their system and I subsequently received a message stating that the amount was credited back to my credit card. However, the reserved seats are still showing on my Latam flight itinerary, so I hope that they are indeed reserved. I did try a dummy purchase for our flights on the Latam website and our reserved seats do show as occupied - so a good sign! After all the problems with their website and useless calls to customer service, I deserve getting the reserved seats at no costs.
About 50% of the time, the Latam agents did not speak understandable English. But of course, it was more than my Spanish.