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Preprint . 2026
License: CC BY
Data sources: Datacite
ZENODO
Preprint . 2026
License: CC BY
Data sources: Datacite
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Improving Kimbundu–Portuguese Neural Machine Translation through Fine-Tuning of Multilingual Models

Authors: Ramalheira, Lirio; Costa, Alexandre; Rodrigues, Cristiano V.; Chau, Franscisco I.;

Improving Kimbundu–Portuguese Neural Machine Translation through Fine-Tuning of Multilingual Models

Abstract

Neural Machine Translation (NMT) systems have achieved strong performance for highresource languages; however, many African languages remain underrepresented due to the scarcity of high-quality parallel data. Kimbundu, a Bantu language spoken in Angola, is one such low-resource language with limited machine translation support.In this work, we introduce a manually curated and humanreviewed Kimbundu–Portuguese parallel corpus and investigate its use for fine-tuning multilingual NMT models. By leveraging the NLLB200 (600M) architecture, we employ parameterefficient fine-tuning with QLoRA to adapt the model to the Kimbundu→Portuguese direction. Experimental results on a professionally reviewed test set of 1,000 sentence pairs demonstrate substantial improvements over strong multilingual baselines, with gains of +10.1 BLEU and +13.2 chrF. Furthermore, semantic metrics—including COMET, AfriCOMET, and BERTScore—show consistent growth, while qualitative analysis confirms better handling of Kimbundu’s complex morphology. These findings suggest that high-quality human reviewed data, combined with efficient fine-tuning, is a viable path to bridging the digital divide for low-resource African languages.

Keywords

Fine-tuning, Multilingual language models, Low-resource languages, Machine translation

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
0
Average
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