Some locales have missing or incorrect translations

I am using scheduler in an Angular application and I have these issues with locales:

1. Serbian, serbian cyrillic, bosnian, croatian, macedonian and many other locales do not have a translation for a year
2. Bosnian and macedonian locales have bad month names, like M03, M04…
3. Serbian locale has header translated in latin, with month and day names in serbian cyrillic
4. Montenegrin locale with ‘me’ key is missing in locales. It should be created as me.js like this:

(function(global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined'
    ? (module.exports = factory())
    : typeof define === 'function' && define.amd
    ? define(factory)
    : ((global = global || self),
      ((global.FullCalendarLocales = global.FullCalendarLocales || {}), (global.FullCalendarLocales.me = factory())));
})(this, function() {
  'use strict';

  var me = {
    code: 'me',
    week: {
      dow: 1,
      doy: 7 // The week that contains Jan 1st is the first week of the year.
    },
    buttonText: {
      prev: 'Prethodni',
      next: 'Sljedeći',
      today: 'Danas',
      month: 'Mjеsеc',
      year: 'Godina',
      week: 'Sedmica',
      day: 'Dan',
      list: 'Planеr'
    },
    weekLabel: 'Sed',
    allDayText: 'Cijeli dan',
    eventLimitText: function(n) {
      return '+ još ' + n;
    },
    noEventsMessage: 'Nеma događaja za prikaz'
  };

  return me;
});

Adding new language only translates the buttons in the header of the scheduler. Month names and day names all render in default english. How and where do I translate these, without external libraries like moment.js and luxon?

How do I translate a custom button’s text that’s added to the header?

According to Release notes, a date-formatting plugin or function should be used instead. This page is pretty confusing, without any useful information on how to solve my issue. It only shows info on formatting, but no info on translating.

Where are current day and month names stored internally for the existing locales, mentioned as 1. above?

[micobarac]

If I add a custom button to the header, how do I localize it?

    customButtons: {
      resource: {
        text: 'resource',
        click: (info: any) => {
          console.log(info);
        }
      }
    }

I’ve tried adding the translation into a locale file:

    buttonText: {
      prev: 'Prethodni',
      next: 'Sledeći',
      today: 'Danas',
      month: 'Mеsеc',
      year: 'Godina',
      week: 'Sedmica',
      day: 'Dan',
      list: 'Planеr',
      resource: 'Resurs'
    },

but, it doesn’t work 😦.

[micobarac]

However, those translations are incomplete / faulty for the locales I have mentioned above, which makes localization of Fullcalendar messy thing.