Translation:Who can write this word in German?
my russian roommates told me that you absolutely have to say написать here, that писать plainly doesn't work. I'm guessing though, that the purpose of написать is to show that it's just like, one word, and you're writing it down once, and that's it. using писать would be like saying "who can be writing this word?" or something among those matters.
really just came across to this conclusion by comparing it to говорить and сказать. I dunno if говорить doesn't work here at all, but if you compare it to english, you don't speak a word, you say a word. even though (according to the mates) you wouldn't say он говорит слово but он выговорит слово, if I understood right.
You use the perfective (написать) here instead of the imperfective (писать) because you are completing a specified action; i.e., writing this word in German, rather than just writing in general. Я пишу = I write (in general), or I'm writing (at this moment). Я напишу новый роман моим уважаемым читательям = I'm writing a new novel for my esteemed readers.
"to write down" is a kind of emphatic, meaning "to very accurately write something that someone else is saying", or to immediately write something one is thinking seriously about. It is a ponderous and portentous way of writing which involves a lot more than simply writing one unknown word in German, without more.
It's possible to use it for one word in German, but that word would be of some significance, at least to someone. The thing written doesn't itself have to be serious, but the endeavor of writing it (down) correctly is important.
This word = Это слово (meaning that the word is close to the speaker and the person he speaks to, for example, it is written on the blackboard or a person can read it in the book in his hands)
That word = То слово (meaning the word can be seen on a sign or something in a distance)
As a native Russian speaker I wouldn't recommend to translate this case as "THAT word".