CorIL: Towards Enriching Indian Language to Indian Language Parallel Corpora and Machine Translation Systems
Abstract
India's linguistic landscape is one of the most diverse in the world, comprising over 120 major languages and approximately 1,600 additional languages, with 22 officially recognized as scheduled languages in the Indian Constitution. Despite recent progress in multilingual neural machine translation (NMT), high-quality parallel corpora for Indian languages remain scarce, especially across varied domains. In this paper, we introduce a large-scale, high-quality annotated parallel corpus covering 11 of these languages : English, Telugu, Hindi, Punjabi, Odia, Kashmiri, Sindhi, Dogri, Kannada, Urdu, and Gujarati comprising a total of 772,000 bi-text sentence pairs. The dataset is carefully curated and systematically categorized into three key domains: Government, Health, and General, to enable domain-aware machine translation research and facilitate effective domain adaptation. To demonstrate the utility of CorIL and establish strong benchmarks for future research, we fine-tune and evaluate several state-of-the-art NMT models, including IndicTrans2, NLLB, and BhashaVerse. Our analysis reveals important performance trends and highlights the corpus's value in probing model capabilities. For instance, the results show distinct performance patterns based on language script, with massively multilingual models showing an advantage on Perso-Arabic scripts (Urdu, Sindhi) while other models excel on Indic scripts. This paper provides a detailed domain-wise performance analysis, offering insights into domain sensitivity and cross-script transfer learning. By publicly releasing CorIL, we aim to significantly improve the availability of high-quality training data for Indian languages and provide a valuable resource for the machine translation research community.
Keywords
Cite
@article{arxiv.2509.19941,
title = {CorIL: Towards Enriching Indian Language to Indian Language Parallel Corpora and Machine Translation Systems},
author = {Soham Bhattacharjee and Mukund K Roy and Yathish Poojary and Bhargav Dave and Mihir Raj and Vandan Mujadia and Baban Gain and Pruthwik Mishra and Arafat Ahsan and Parameswari Krishnamurthy and Ashwath Rao and Gurpreet Singh Josan and Preeti Dubey and Aadil Amin Kak and Anna Rao Kulkarni and Narendra VG and Sunita Arora and Rakesh Balbantray and Prasenjit Majumdar and Karunesh K Arora and Asif Ekbal and Dipti Mishra Sharma},
journal= {arXiv preprint arXiv:2509.19941},
year = {2025}
}