Many Americans and Japanese feel that people from the two countries have different styles of speaking, and they are probably right, but not so right that they are really "inscrutable" to each other. Americans often say that Japanese conversation is indirect, that people talk around the point without directly stating it, and that Japanese people are reluctant to say "no" directly. It often seems to Americans that they have to work hard to realize what Japanese are really talking about. Japanese people say that their talk is subtle and requires them to be conscious of cues that are not spoken, of body language and facial expression, and of signals of the emotional state of the other person. They feel that communication is difficult and that listeners in particular have to be very careful about interpreting what speakers say.
Communication is difficult, and both speakers and listeners have to work at it in both cultures, but both Japanese and English give people a number of tools to use in accomplishing communication, sometimes same and sometimes different. Also, people using the two languages must pay conscious attention to different features of each language.
There are some grammatical differences between the two languages that make Japanese seem more vague and English more specific to people who learn the other language. For instance, most English sentences require that a speaker use both a subject and a predicate in forming the sentence. But actually, one can think of lots of exceptions, especially in casual speech. And most commands and requests don't use a subject because the subject is "understood."
When English speakers choose a noun, they have to decide if it needs to be used with "a" or "the" or no marking at all.
A cake is needed for a wedding or birthday party.
Cake is good for breakfast, too.
The cake didn't turn out too well.
English speakers also need to decide how to mark singular and plural on nouns and predicates. If they are talking about people (and some other things or animals), they need to show whether they are talking about males or females if using pronouns. These distinctions are not required in Japanese. Nouns are the same whether they are singular or plural, pronouns are seldom used except for people, and even those are often left out ("understood"). If it's really important, and not obvious from the context, Japanese does have ways of making clear whether singular or plural number is meant, but plural marking isn't used if explicit reference is clear or unimportant.
It turns out to be easy to learn how NOT to do these things when English speakers are learning Japanese, and most learners are amazed at how little difference in comprehension it makes if those things that are required in English are just left out. But for Japanese speakers who are learning English, it is much harder to remember to put all that information into every sentence, so it makes English seem much more detailed and specific to them. But understand that, while English is detailed in some areas, Japanese is detailed in other areas, so it is hard to say which language is more explicit.
Verbs in English, too, have to agree with the subject in number, though that makes no difference to the verb form in Japanese. English has different systems of verb tenses (things like past "ate" and present/future "eat, will eat") and aspects (things like "is about to fall," "is falling," "keep falling," "have just fallen,"). Japanese learners of English have to learn to think about these, and English speakers learning Japanese have to learn how to use Japanese system of tense and aspect.