My colleague just told me that it's incorrect to say >
"I am an English and Spanish teacher."
He said it's correct to say >
"I am a English and Spanish teacher."
He said that I have to use 'a' because of the word 'Spanish'.
The only idea I have is one you're going to like: You are right and your friend is wrong. The articles a and an must agree with the initial sound of the word that immediately follows it. A goes with Spanish and an goes with English.
I am a Spanish and English teacher.
I am an English and Spanish teacher.