"Julia is studying to become an English teacher."
Translation:Julia étudie pour devenir professeure d'anglais.
@Doggyddodo1: The subtlety is that professions do get an indefinite article if they are modified: Je suis un grand professeur (at least in my dreams). But while English speakers think of "English" as directly modifying "teacher", in French d'anglais is a separate prepositional phrase that doesn't prompt the use of une.
The confusion is that we use the word "to" in (at least) two different ways in English. When we say "to X" in English, we often mean "in order to X". The verb devenir is the infinitive verb "to become", but it doesn't mean "in order to become". You need to add pour to show that the studying is for the purpose of (or in preparation for) becoming a teacher.