"How to become her friend?"
Translation:Comment faire pour devenir son ami ?
I think this is bad English. We say "How do I become her friend?" "How do you become her friend?" "How does one become her friend?" The given sentence is the title of an article perhaps, but not good spoken or written English. "What should I do to become her friend?" is also better English. So, you cannot translate the French " Comment faire pour devenir son ami ? " directly into English, you give the equivalent well-phrased English question.
"comment faire pour devenir" mirrors something like "what shall I do to become..." or "how shall I proceed to become...?" or the shorter version "how to become...?"
In French, infinitive verbs are often used with an interrogative word: "que faire, comment faire, pourquoi faire, où faire... ?", all being impersonal, whereas in English, you would probably use a conjugated verb, like "what/why/how/where shall I...?"
"Comment faire, pourquoi faire, où faire, quand faire...": an interrogative + an infinitive is a very common way of asking an impersonal question in French. This is what you are learning here and you cannot guess it if you are not shown this direct translation, which will mechanically be used in the reverse exercise.
However, a few other natural English translations are accepted of course, including the one you are mentioning.
Very helpful. Apparently in French, sentences do not have to be complete sentences in the English sense to pass muster in French? Is that new or a style issue? I was reading some french comments in a light periodical on the web and there were quite a few comments that were not full sentences in the English grammar sense. More apositional phrases I think is the term. Is that traditional in literature or new or perhaps just casual? it's how we think, but is it also ok in French to write or speak in phrases non-casually?
I think we consider such questions in infinitive as complete sentences.
Otherwise, other cases of fragments ending with a full stop are common in contemporary French writing.
In speech, a lot of sentences are incomplete, and ellipses are common; as long as your counterparts understand you, you may not need to fully develop your sentence.
However, it is difficult for someone learning French to identify what you can skip and what not.