I needed to change the words "Certificate of Achievement" for "Certificate of Completion" which I was able to do by editing the certificate.php under the mod/certificate/lang/en_utf8 directory.
The problem is that when the students take the course in Spanish by forcing the language option in the course, the certificate is printed in Spanish, but I can't find the Spanish langugage block anywhere, so I can modify the php file and change the wording.
The plugin comes in 4 languages, English, Italian, Portuguese, and Dutch (or German?) however for some reason the certificate still prints in Spanish.
Does anyone know where I is the file I need to modify to change the words in Spanish?