"We are reading a book."
Translation:Εμείς διαβάζουμε ένα βιβλίο.
Greek is a proboun-drop language which means you can have the option to add in or take away/ignore any personal pronouns in a sentence, like Italian, Spanish, Portuguese, Hungarian, Catalan, Romanian, etc. For example:
With pronoun εγώ: "Εγώ είμαι ένας άντρας."
Without pronoun εγώ: "Είμαι ένας άντράς."
Εμείς διαβάζουμε can be translated as either “we read” or “we are reading”, according to context and the rules of English grammar. There is no distinction in Greek.
You can also leave out the subject pronoun (since the subject is clear from the verb ending) and say just διαβάζουμε, which can also be translated in both of those ways.