Unfortunately, python doesn't have good built-in support for formatting dates in locales other than the current one. You can temporarily switch locales, but that's not a great solution. 
You can use the the Babel package to format the dates, though it doesn't provide precisely the same value you expect -- the case is slightly different.
For example, you could create a keyword that dates a month, year, and locale, and returns the formatted version. 
First, create a python file named CustomKeywords.py with the following contents:
# CustomKeywords.py
import datetime
from babel.dates import format_date
class CustomKeywords:
    def get_date_for_locale(self, locale, year, month=1, day=1):
        d = datetime.date(int(year), int(month), int(day))
        return format_date(d, "MMMM Y", locale=locale)
Next, import this library into your test case and then call get date for locale to get the date for a given locale:
*** Settings ***
Library  CustomKeywords.py
*** Test Case ***
Vietnamese
    ${date}=  get date for locale  vi_VN  2017  7
    Should be equal  ${date}  tháng bảy 2017
Thailand
    ${date}=  get date for locale  th_TH  2017  7
    Should be equal  ${date}  กรกฎาคม 2017