That depends on your technical skills and your budget. If I had to do this, I might try one of the following methods:Hashimi wrote:What is the best way to do this?
a) Use approximate string matching
1. Translate the whole list with DeepL to English and save the Spanish and English words in a spreadsheet file.
2. Use the Levenstein distance or a proper Fuzzy Matching algorithm to calculate the similarity between the two words. E.g., manera <=> manner; Levenstein distance = 2; similarity ≈ 67%. (Words that start with the same letter and have a similarity of ≥ 65% are most likely cognates.)
b) Use an existing cognate list
1. Several text books contain English-Spanish and/or Spanish-English cognate lists, for example, Resnick, Seymore - Essential Spanish Grammar.
There are also lots of cognate lists on the Internet, for example, this one.
2. It should be relatively easy to OCR them and to check the entries in the RAE list against them.
c) Outsource the task to low-cost websites, e.g. Amazon Mechanical Turk or fiverr.