Do human populations differ in core body temperature?
Yes there are different physiological temperatures in different ethnicities. To know which temperature range differences are inherited and which are learnt by living in different climates requires surveys of people who are from the same region. 

This study states a 0.35 degrees difference between a japanese and a malaysian, 36.95 and 37.3, it's alot.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3929238/

The following study states states a 0.15 degree difference measured with similar precision,
https://www.ncbi.nlm.nih.gov/pubmed/20824480

This graph shows that the human body temperature is 36.2 at rest, at night/morning and 37.5 in the middle of the day. : 
http://millar.bio.ed.ac.uk/andrewM/WE%20book99/Part2-examples.html#tth_sEc8.3.4.2 

That may account for the 1 degrees difference in Japanese studies, they measure first thing in the morning/ at rest/at night, and japanese body temperature of 0.15-0.35 lower that some other ethnic groups.

There are geographic differences if you test the homeostasis response of different populations, the inner body temperature responses, the temperature of the extremities, sweating responses, the physiological responses and the blood cell characteristics.

Mitochondria has also been shown to be selected by climate type. Populations living in colder environments have lower mitochondrial diversity and that the genetic differentiation between pairs of populations correlates with difference in temperature, and they have found certain genes mutations in the ND3 and ATP6 that seem to be independantly implicated in similar climate adaptations. 

The temperature is measured in lots of zones of the body and of the extremeties and the capillary flow. That doesn't account for habituation and acclimatization to tropical or northern climates.  

The tropical population was found to have different thirst and sweating efficiency, and to change temperature at different rates to compensate for the same ambient conditions and exercise.

Some schools in China enforce that children run around in shorts in the snow in the winter and at playtime so that they regualte their body in the cold. Some northern people are apparently able to override the unconcsious response of the physiology that can raise body tempereture very effectively, and be able to hold in cold tanks for surprisingly long times.

Cold and hot weather are a strong force on natural selection, as illustrated by mitochondrial adaptations, because an advantageous in temperature regulation brings about a global performance advantage. The physiology of temperature regulation has been subject to many theories and studies, and they have found physiological conditionings can be honed by genetic adaptations in different populations.

Even chimpanzees have similar temperatures:

The cycles of increasing and decreasing body temperature of chimps
are exponential and symmetrical, with an amplitude of 2.6-2.9?F
(2-3 AM - 2-3 PM) and a 24-hour mean of 99.0?F, or 98.7?F. The S.D. of the 17 daily means was 0.53?F; and
of the values at any single hour, 0.63'F....Thus, in the bulk of the species the temperature ranges daily from
37.5- to 39+?C whereas the ordinary range in man is 36.5 to 37.5?C. Low
values are similarly reported for several primitive primates.

some references: http://rspb.royalsocietypublishing.org/content/276/1672/3447  https://www.jstor.org/stable/1377087  

Actually this study states a 0.35 degrees difference between a japanese and a malaysian, 36.95 and 37.3, and study referenced afterwards states states a 0.15 degree difference, 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3929238/

https://www.ncbi.nlm.nih.gov/pubmed/20824480