JSFiddle - React, Tailwind, and code Playground

HTML

<div>Diskuze obsahuje 1 <span class="comment" data-count="1" data-plural-1="komentář" data-plural-2="komentáře"><span>komentářů</span></span></div>

<div>Diskuze obsahuje 2 <span class="comment" data-count="2" data-plural-1="komentář" data-plural-2="komentáře"><span>komentářů</span></span></div>

<div>Diskuze obsahuje 5 <span class="comment" data-count="5" data-plural-1="komentář" data-plural-2="komentáře"><span>komentářů</span></span></div>

CSS

span[data-count='1']:after
{
    content: attr(data-plural-1);
}
span[data-count='2']:after, 
span[data-count='3']:after, 
span[data-count='4']:after 
{
    content: attr(data-plural-2);
}

span[data-count='1'] span, 
span[data-count='2'] span, 
span[data-count='3'] span, 
span[data-count='4'] span
{
    display: none;
}