I started by spellchecking each column on a letter by letter basis: the As, the Bs, the Cs... It really demanded added concentration because I had to check each column, row by row. And the content of each column is very distinct from the another: English word, the corresponding Portuguese sound, and the meaning(s) in Portuguese.
At the end of letter E, I decided to change my strategy, hoping to simplify it. First I copy-pasted all the English words into a separate Excel sheet and did a spell check... Done! Any editing was also done immediately in the master sheet.
Then I copy-paste all the sounds of the following letter on a separate sheet and carefully check the details. Is the pronunciation in synch with my way of pronouncing the word? Are the diphthongs and some "th" sounds underlined? Are the same sounds consistent throughout?
Finally, I copy-paste the sounds of the words of that same letter in another sheet and carefully checked each word myself, because I don't have a Portuguese dictionary in my spellcheck software. :-(
This seems like a good strategy. It's working well. There may be others, of course, but it is the first time that I'm doing this type of proofreading, so I had to decide what felt more efficient and easier.
As you can imagine, I need to be 100% focused on each part I deal with. It's kind of looking at each word of each column through a magnifying glass. I take a few breaks in order to disconnect or distance myself for a few minutes, which seems to help me notice typos more easily. Naturally, this doesn't guarantee that there won't be any.
I think I'm a bit behind in my work. I had to interrupt a few days last week because of high blood pressure. It seemed best to take it easy. There's no need for stress!
And now... it's Christmas time! :-) Preparations at home and at my parents' are my priority.
Hopefully, though, it'll be smooth sailing between Christmas and New Year's, when I hope to catch up.