Since last year, it’s official, thanks to the UN. Here’s what they have to say about this day:

International Translation Day is meant as an opportunity to pay tribute to the work of language professionals, which plays an important role in bringing nations together, facilitating dialogue, understanding and cooperation, contributing to development and strengthening world peace and security.
Transposition of a literary or scientific work, including technical work, from one language into another language, professional translation, including translation proper, interpretation and terminology, is indispensable to preserving clarity, a positive climate and productiveness in international public discourse and interpersonal communication.
Thus, on 24 May 2017, the General Assembly adopted resolution 71/288 on the role of language professionals in connecting nations and fostering peace, understanding and development, and declared 30 September as International Translation Day.

So enjoy, and perhaps thank a translator or interpreter who’s helped you communicate with their work.

(c) LanguageMatters