"Who is talking?"
Translation:Qui parle ?
The basic rule: there is no 'IS' 'ARE' or 'AM' before any "ing". Examples: Wrong: "He is talking" (Il est parle) Right: "He talking" (Il parle) Wrong: "I am going" (Je suis vais) Right: "I going" (Je vais).
If there is no "ing" then you put 'IS' 'ARE' or 'AM': Right: "I am red" (Je suis rouge) Wrong: "I red" (Je rouge) Right: "I am pretty" (Je suis jolie) Wrong: "I pretty" (Je jolie)
Hope it makes sense.
If you wanted to translate word for word, it would be "il est parlant" (present participle or gerund).
However, that verbal form does not exist in French to express a continuous action.
Therefore, if you are given "who is talking?" you have to translate either "qui parle ?" or "qui est en train de parler ?", where être en train de + infinitive is the expression which best expresses that the action is in progress at the time you speak.
You cannot choose to translate word-for-word and end up with a correct translation here. The French "qui parle ?" is conjugated according to French rules or grammar and the English "who is speaking?" is translated according to English rules of grammar. One cannot take a word-for-word translation such as "est parlant" and expect to end up with a correct translation.
You need to know how to conjugate verbs in English as well as French. Qui parle may be translated as "who speaks" or "who is speaking". From English (since you know there is no present continuous in French), you will translate it to French Simple Present. I.e., you do not translate every single word. You translate the meaning.