How can you tell what question word Ĉu is supposed to represent? I put down "can the men speak Esperanto" which was marked wrong, but I'm not sure the proper translation for Ĉu. It's supposed to introduce a question, but how do I know how to translate it when it could stand for basically any question word?
In yes/no (and either/or) questions, Ĉu doesn't represent any word which can be expressed in English. It simply means "this sentence is a question." You can think of it as representing the change in word order which changes a statement to a question in English.
- I am a big man = mi estas granda viro
- Am I a big man? = cxu mi estas granda viro?
In some cases, English makes it harder on us.
- The men speak Esperanto - Speaketh the meneth Esperanto?
- The men do speak Esperanto - Do the men speak Esperanto?
- La viroj parolas Esperanton - Ĉu la viroj parolas Esperanton?
This is a quirk of English, not of Esperanto.
Sometimes it helps to think that "Ĉu" means "is it true that" - which works for yes/no questions.
- Ĉu la viroj parolas Esperanton = is it true that the men speak Esperanto?
but not for either or
- Ĉu la viroj parolas Esperanton au la francan? Do the men speak Esperanto or French.
As always, make sure you present your answer in natural sounding English when typing to Duo.
To further clarify, "can" would translate with some form of povi (to be able), so "Can the men speak Esperanto?" would be, "Ĉu la viroj povas paroli Esperanton?"
(Note that parolas changes to paroli. When you have two verbs in a row like this, the first is conjugated and the second is in the infinitive; this is true in most European languages, not just Esperanto.)
The name Esperanto is capitalized in Esperanto to distinguish it from the word esperanto. With a capital E it's the name of the language. With a lower case e it's means "one who hopes." The other thing you'll notice is that most language names look like adjectives. (la germana, as you pointed out.) There are a few languages (latino, sanskrito) which can be referred to as nouns, but I'm pretty sure none of them are capitalized.