The celebrations have been promoted by FIT (the International Federation of Translators) ever since it was set up in 1953. In 1991 FIT launched the idea of an officially recognised International Translation Day to show solidarity of the worldwide translation community in an effort to promote the translation profession in different countries (not necessarily only in Christian ones). This is an opportunity to display pride in a profession that is becoming increasingly essential in the era of progressing globalisation.
According to the International Translators Association (you can find more information on the International Translation Day here),
[…] the challenge of International Translation Day remains the same: to raise awareness of the translation profession.
For those who didn’t know, St. Jerome is the patron saint of archeologists, archivists, Bible scholars, librarians, libraries, schoolchildren, students and translators. You can read about his life and works on this Wikipedia article. Last year, Jill Sommers posted a very detailed post about him, which was also about the way he worked as a translator (he revised and translated parts of the Bible into Latin, and awarded sainthood thanks to the services he rendered to the Church). Quoting the article posted on the TIHOF’s website:
Jerome’s humility regarding his own work set a good example for translators who followed him. He freely admitted ignorance, even embarrassment, when warranted, and revisited some of his translations, making corrections and additions. On the other hand, he also pointed out that a translation’s accuracy depended greatly on the reliability of the source text: copyists often inadvertently introduced errors, which would be compounded and passed down through the centuries.
The International Translation Day has a different theme every year. This year’s theme is Working Together.