"The couple has a son."
Translation:Das Paar hat einen Sohn.
Warum ist es nicht "einem Sohn" ich hatte gedacht wann ein Noun ist Maskulin ein geht zu eine[m]... mein Satz erklärt auf Englisch:
Why is "einen" and not "einem" correct? I thought when the noun is masculine the word before it should end always in "em" and when feminen end in "en"!
Danke im Voraus!
In general, either a singular or plural verb is acceptable with a collective noun as the subject in British English.
Gowers (1) notes that the plural verb is more desirable when the emphasis is on the members, and the singular when the emphasis is on the body as a whole. He also notes that a grammatical or stylistic need to employ a particular pronoun may settle it one way or the other, and that a singular verb can be used with lexically plural subject if the plural-looking noun denotes a single entity (eg, "The United States is launching a probe to Mars"), but that does not apply here.
(1) Gowers, E (1987) et al. The Complete Plain Words. 3rd ed. London: Penguin.
It's grammatical in American English.
Duolingo is an American web site, so its primary English is American English. As you are using the site to learn German, translating from an American usage or spelling isn't really an obstacle, I would have thought, even when that usage isn't common in British English (this one, of course, is widely used in British English anyway). When translations go the other way, in most cases British English spellings have already been added as alternatives. Where they have not yet been added, you can flag them up to be added through the facility for that.
I don't understand what difficulty you were caused in this particular example. Did you put in the plural verb as a translation and have it rejected? I thought when I tried that it allowed it.