@Ruslan - You mean past/present/future verb tenses, right? The 2 languages I study that don't have them are Thai and Mandarin.

@Pedro Simões - You're completely wrong. Please don't just make stuff up to post things here, because it can mislead others.

@Pedro Simões-Of course they have a grammar. The last question, I don't know how to say it. I mean,  if we do not use tenses,  are there any problems in communicating to other people? will it make misunderstanding among the people who are talking to?

@aegis- That's right. I'm Indonesian, I don't see a past/present tense in Indonesia, but there's an exeption in future tenses  If I want to say something, I just only give a preposition of time, for example I eat yesterday, I eat today, but if i want to say eat in tomorrow, in Indonesia, i will say "saya akan makan besok pagi/I will eat tomorrow).

I' still learning English, if i make mistakes, please correct my words. I will appreciate it.

as @aegis said, Chinese or Mandaren doesn't have any tense. we just put the time like yesterday,tomorrow, etc into the sentences. there's no problem for us of course. but im not sure if the students who are from other countries would find it easier.

We also don't have tenses in Vietnamese. I agree that there aren't any problems with it. In fact, it makes things easier for people wanting to learn the language. I know many people struggle with past perfect/present perfect/future perfect/etc in English, but languages without tenses just take away that headache.

Ruslan, when I first saw the post, I thought the Indonesian language must have a time reference.  

I thank you and aegis for this information