Let's not forget the RCC found Jan Hus guilty of heresy for his efforts to preach in the vulgar tongue and his declaration of sola scriptura.
No, the reason why St. Jan Hus and St. Jerome of Prague were burned at the stake was their attempt to restore what had been lost in Czechia (but still existed in parts of Slovakia among the Rusyn people in the Tatras) after the Austrians conquered it - the Orthodox model of liturgical worship, which included preaching in a language the people could understand (which for some people in the 14th century, such as Italians, Latin would fit into that category, but for Slavs, Latin was incomprehensible; they were accustomed to worshipping in Church Slavonic, a pan-Slavic langauge designed for maximum mutual intelligibility, written primarily in an alphabet designed by St. Cyril based on the Greek alphabet (although in Croatia, some spoke Galgolithic, which difffered from Church Slavonic only in that it was written in a modified Gothic alphabet), and communion in both kinds (indeed, all of the Czech Protestant groups, from the most extreme Taborites, whose views were like those of future low church Protestants, to the most conservative Utraquists, agreed on the importance of the faithful receiving both the Body and Blood of our Lord in the Eucharist, rather than receiving only the Body). This is understandable, for a people who had 250 years previously been receiving in both kinds according to the Divine Liturgy of St. John Chrysostom; whereas in subsequent political events that resulted in Eastern Orthodox people becoming part of the Roman church, the Roman church ensured that Byzantine Rite worship was retained, for example, in the formation of the Polish-Lithuanian Commonwealth, in the case of the conquest of Prague, that didn’t happen.
It is for this reason that the Orthodox Church of the Czech Lands and Slovakia venerates St. Jan Hus and St. Jerome of Prague as martyrs.
That being said, the Roman church repented of that after Vatican II, although conversely I would argue that the reforms of Annibale Bugnini were poorly conceived and poorly implemented, and the 1965 missal and the 1967 Dominican breviary represent the intent of Sacrosanctum concilium (which I don’t agree with entirely, for example, the suppression of the ancient office of Prime, which was historically so important that people would learn to read and also learn the Latin language using the example of that office, with books called Primers; also Prime is particularly beautiful among the “Minor Hours” and the only ancient liturgical rites that lack it are the East Syriac Rite (which may have had it in the form of a lost monastic rite, but in the surviving rite, which is a cathedral rite, interestingly the Church of the East is the only church where the Islamic persecution resulted in the loss of the monastic rite rather than the cathedral rite, there are only the three ancient offices of Vespers, Compline and Matins, and then, oddly enough, and as far as I can tell, coincidentally, the West Syriac Rite, which has the Third, Sixth and Ninth hours but no First Hour. Although I am still researching to try to find out if that was always the case or the result of some abbreviation.
By the way nothing in this thread is intended as anti-Catholic polemic, for I love the Roman Catholic Church as should be evident; indeed I love all traditional liturgical churches, and even some non-liturgical churches.