JSFiddle - React, Tailwind, and code Playground

JavaScript

var lang = {
        "%{followers_count} followers": "%{followers_count} följare",
        "%{name} on Twitter": "%{name} på Twitter",
        "10k unit": "10k",
        Follow: "Följ",
        "Follow %{name} on Twitter": "Följ %{name} på Twitter",
        "Follow %{screen_name}": "Följ %{screen_name}",
        "This page has been shared %{tweets} times. View these Tweets.": "Den här sidan har delats %{tweets} gånger. Visa dessa tweets.",
        Tweet: "Tweeta",
        "Tweet %{hashtag}": "Tweeta %{hashtag}",
        "Tweet to %{name}": "Tweeta till %{name}",
        "You are following %{name} on Twitter": "Du följer %{name} på Twitter"
    };
function _(literal) {
    return literal in lang ? lang[literal] : literal;
};

var v = {
    lang: 'en'
};

function H(e) {
  var t, n, r = parseInt(e, 10), i = new RegExp("^\\" + _(",")), s = {ja:1, ko:1};
  return isNaN(r) ? "" :
    r < 1E4 ? r.toString()
      .split("")
      .reverse()
      .join("")
      .replace(/(\d{3})/g, "$1" + _(","))
      .split("")
      .reverse()
      .join("")
      .replace(i, "") :
        r < 1E5 ? s[v.lang] ?
        (n = (Math.floor(r / 100) / 100).toString(), n + _("10k unit")) :
        (t = (Math.round(r / 100) / 10).toString(), t.replace(/\./, _(".")) + _("K")) : _("100K+")
}

console.log(
    H(15),
    H(155),
    H(1555),
    H(15555),
    H(155555)
);

// it prints out
// 15 155 1,555 15.6K 100K+