Learn Portuguese (Portugal): Procuro um tradutor que fale inglês. - I am looking for a translator who speaks English.

This is the core of your current lesson! You use the subjunctive in a relative clause (the part starting with que) when you are talking about someone or something indefinite, uncertain, or non-existent. Because you are looking for any translator (um tradutor) and don't know who they are or if they even exist yet, you must use the subjunctive fale.

What happens if I change um tradutor to o tradutor (the translator)?

If you change it to o tradutor, you are now talking about a specific, known person (a definite antecedent). Because you know this person exists, the verb in the que clause must switch back to the normal present tense (indicative). The sentence would become: Procuro o tradutor que fala inglês.

Why is there no preposition after Procuro? Shouldn't it be "Procuro por"?

English speakers often want to add por to translate "for" in "look for". However, the Portuguese verb procurar already inherently means "to look for" or "to search for". Adding por right after it is redundant and unnatural.

Why is inglês written with a lowercase "i"?

In Portuguese, the names of languages and nationalities (as well as days of the week and months) are not capitalized unless they appear at the very beginning of a sentence.