Career
He was part of the Zois circle, a group of Carniolan scholars and intellectuals that were instrumental in the spread of Enlightenment ideas in the Slovene Lands. His translations of the Bible, based on the 16th-century translation of the Lutheran author Jurij Dalmatin, set the basis for the development of modern standard Slovene. He was ordained a Roman Catholic priest in 1769 in Trieste, where he served until the Suppression of the Jesuits in 1773.
He then became the personal secretary of Bishop of Ljubljana Karl Herberstein.
Under Herberstein"s influence, Japelj became sympathetic to Jansenist ideas. With the support of Bishop Herberstein, Japelj started translating religious texts into Slovene.
Together with Blaž Kumerdej, he began a new translation of the Bible in Slovene, based on Jurij Dalmatin"s translation from the 1580s. In 1807, he started compiling a grammar of Slovene, which, however, remained unfinished.
He also translated several poems by Metastasio, Kleist, Racine, Hagedorn, and Pope into Slovene.
In 1799, Japelj became the director of the seminary in Klagenfurt, where he also covered other positions in the ecclesiastical and civil administration. He died in Klagenfurt in 1807, shortly after being appointed bishop of Trieste.