Hai is one example. There is no distinction between singular or plural in Japanese. Moreover, gender is not indicated grammatically. However, vocabulary varies according to whether a man or a woman is speaking. Word order in Japanese may also pose some difficulties for the learner.
Verbs usually come at the end of the sentence, instead of near the beginning as in English.
Since there are no relative pronouns, sentences tend to be long and complicated. Particles are difficult, too. All the words in a Japanese sentence are connected by these tiny word fragments, which define the grammar of preceding words. Pronunciation is dramatically different in Japanese than it is in English. Since all Japanese words end in vowels, learners may have to spend quite a long time practicing them to get the hang of the rhythm.