Brazil's most populous

[Paucle]

replace last letter of first word with an "N"

[Staley]

If someone asked, I was going to say "pretend it's Spanish."

[quimboat]

Boy, this one was all over the place. The answer it finally accepted isn't anything close to Portuguese.

For anyone still attempting it, replace the last letter of the first word with an 'n', per Paucle's instruction above, and the third letter of the second word with a 'u'.

[Paucle]

most sources have that as a "u"; what's it supposed to be? O?