I assume you are talking about the plural (one month, two months). Plurals are more difficult for Chinese and Korean speakers because neither of those languages use a plural form. 《一月，二月》。 As for saying the words, the "th" sound and "s" sound are hard to say together, even for native English speakers. So "months" would be spoken more like "munts". It's the same way with many phrases. For example, the phrase "I don't know", would usually sound like "I duh noe", unless the person is trying to make a strong point.

you mean possessives? i will give you one month's salary. that five months' worth of studying did nothing for me!