The 'International Translation Day' has been observed across the world every…

Concept: International Translation Day recognizes the work of language professionals worldwide. It was established by the International Federation of Translators (FIT) in 1991, with the date fixed as 30 September — the feast day of Saint Jerome, the scholar who translated the Bible into Latin (the Vulgate) and is honoured as the patron saint of translators.

Application: The question asks for the date observed every year since 1991 — this points to FIT's original 1991 designation of 30 September. The United Nations General Assembly later reaffirmed the same date through Resolution A/RES/71/288 (2017), which formally recognized 30 September as International Translation Day at the UN level without changing the date.

Cross-check: None of the other offered dates carries the translation-day designation:

• 30th August is observed internationally as the UN Day for the Victims of Enforced Disappearances, unrelated to translation.

• 31st August is designated by the United Nations General Assembly as the International Day for People of African Descent (2020), also unrelated to translation.

• 26th November is observed in India as Constitution Day (Samvidhan Diwas), commemorating the adoption of the Constitution in 1949 — a separate observance.

Result: Hence, International Translation Day has been observed every year since 1991 on 30th September.