There are 55+ cultures in kerbalrenamer.cfg with firstname for both binary genders. Near the bottom of this file, there are a number of profiles that defines the cultural mix that can be used to generate names for a program.
Due to a quirk with KSP, the initial 4 kerbals are generated from the profile 1951. It is made of nations with some kind of rocket research expertise in 1951. You may edit your own copy if you don't like this mixture.
Select ONE profile from the Settings section for Kerbal Renamer. Whilst it is possible to select more than one (a UI issue), only one will be used.
It is possible to define your own mixture of culture by editing the weights in the CUSTOM profile, then selecting this profile in the relevant Settings section.
You are welcome to add cultures to kerbalrenamer.cfg by copying another culture, and editing the FFIRSTNAME1, MFIRSTNAME1, LASTNAME1, optionally FLASTNAME1 (last name for women). Such edits can be shared with the community through a Pull request. If the culture places surnames before first names, use the config node value pattern = LF as with China and Hungary.
The cultural coverage in kerbalrenamer.cfg is derived from frequency dataset and largely covers Northern hemisphere nationality. The nations relevant to the 1951+ space race are covered. There are also many nations that are not particularly relevant. This being said, there are many missing nations. The choice to include/exclude was pragmatic and based on available data. It certainly is not a thorough enthographic study.
Finally, KSP uses a binary gender system (M/F). We acknowledge that this is an oversimplification.