To get a culture set that you can use as a template, then go into the game's local files and follow this file path:
In here, you should see the following:

• EasternFantasy
  
• WesternFantasy
  
• WorldII

Copy one of these (although which one it is does not matter) and rename the folder, the one you have chosen will be your template.

In the folder you have copied, you should see 3 files:

• CityNames.csv
  
• PoliticalSystems.json
  
• StateNames.csv

csv is a type of file that only uses commas and newlines (or seperate lines) to create data or something. The files "CityName" and "StateNames" both use csv, which would look like this:
notice how every section uses commas to seperate eachother. Now if you open this with a spreadsheet program, then it would automatically convert the commas and newlines into a working organized spreadsheet.

there are 2 parts of this: the Key , which identifies what name it pulled; and Translations (shown as languages like "chinese"), which would automatically change the key into what language the user is using.

Now for example, we pull a part of the csv file and we are shown this to modify:
If we want to modify this, then simply change "K1" to whatever you want, then change "T1" to what it translates to. so it might look like this:
If you want, you can add more translations to it making it available to more users if you want to upload your mod to workshop.

if you wanted to test your culture set, you might have thought to put it in the same folder as where you got your template. Whoever, it would only make the game think its part of the game and not a mod. This results with the game failing to recognize your mod as, well a mod . So what you should do is create a mod folder.

To do this, you will have to (from streaming assets) create this:
Once you got that created, then put your mod in the culture folder, and your done!

Everything should be self explanatory, enough that you can figure it out yourself! Whoever, if your mod doesnt work, then it must be because of one of these reasons:

• (game doesnt work) you modified the csv files incorrectly / you forgot to add commas at the end - what this means is its maybe because you used a spreadsheet program (like me). the issue lies at the end of those lines. when you open those up with notepad after you modified it with excel, then you will see something like " Key,English ". Now the thing missing is the comma at the end of "english", as its supposed to be " Key,English, " WITH A COMMA at the end. If you are unable to resolve this issue, then your game would literaly cease to have the words "fantasy map simulator" in it (it breaks entirely).

so... make sure you:

1. have the csv lines end with commas
   
2. make sure the languages used are spelled correctly, or exists at all

I am not sure about this part, for I have not tried it yet. However I am pretty sure that it works exactly the same as culture sets, so just figure it out from here.

Thank you for reading my yapology, i just decided to make this right after i figured it out because most people are asking about it and received no answers for a long time. if i made a mistake in one of the information i have provided, then tell me