When I enter into dialogue and have speech for example to persuade someone I always fail if my level is not high enough for example [Barter 35/40] every time it fail even with 39/40 it’s a fail, is it bug or it’s new change in game ?

Cheers

Erm... You have 39 in skill... And it requires 40... Just like how Very Hard locks require 100 in Lockpick skill and not 99... So no... It's not broken..

I think I've read in some of the other Fallouts/other games fail/pass can be a somewhat random check...but this isn't the case in NV. You have to have at least the stated amount or you will fail. So as stated...not broken.

It's not like FO3 where you have a chance to succeed no matter what your speech/skill level. In NV you have to meet the minimum speech/skill level to succeed.

As everyone has said the speech check is pass/fail. One clue is that if you can't make it, the item shows red.

I haven't been able to verify whether some of your stats like Intelligence/Charisma/Luck have a bearing on how high the bar is placed. i.e. if you have high Luck and Charisma the skill required is 40, but if they are low the number is 50.