fasttext-langdetect

May 26, 2026 · View on GitHub

fasttext-langdetect is a thin Python wrapper around Facebook's pretrained lid.176 fastText language identification models.

Supported languages

af als am an ar arz as ast av az azb ba bar bcl be bg bh bn bo bpy br bs bxr ca cbk ce cebckb co cs cv cy da de diq dsb dty dv el eml en eo es et eu fa fi fr frr fy ga gd gl gn gom gu gv he hi hif hr hsb ht hu hy ia id ie ilo io is it ja jbo jv ka kk km kn ko krc ku kv kw ky la lb lez li lmo lo lrc lt lv mai mg mhr min mk ml mn mr mrj ms mt mwl my myv mzn nah nap nds ne new nl nn no oc or os pa pam pfl pl pms pnb ps pt qu rm ro ru rue sa sah sc scn sco sd sh si sk sl so sq sr su sv sw ta te tg th tk tl tr tt tyv ug uk ur uz vec vep vi vls vo wa war wuu xal xmf yi yo yue zh

Install

pip install fasttext-langdetect

Requires Python 3.9 or newer. Works out of the box on Linux, macOS, and Windows for Python 3.9 – 3.13 (including free-threaded 3.13t) — no C++ toolchain required, because we depend on fasttext-predict, a minimal prediction-only fork of fastText that ships prebuilt wheels for all major platforms and has no NumPy dependency.

Already have fasttext or fasttext-wheel installed? All three packages provide the same import fasttext module and share install paths. If you previously installed the source-only fasttext package and want a clean upgrade, run pip uninstall fasttext fasttext-wheel first, then reinstall fasttext-langdetect.

Usage

detect accepts any UTF-8 string. Embedded newlines, tabs, and other whitespace are normalized internally — paragraphs and multi-line inputs work without preprocessing. Pass low_memory=True to use the compressed lid.176.ftz model, which trades a small accuracy hit for a much smaller memory footprint.

from ftlangdetect import detect

result = detect(text="Bugün hava çok güzel", low_memory=False)
print(result)
# {'lang': 'tr', 'score': 1.0}

result = detect(text="Bugün hava çok güzel", low_memory=True)
print(result)
# {'lang': 'tr', 'score': 0.9982126951217651}

# Multi-line input is fine — whitespace is normalized internally
result = detect(text="The quick brown fox\njumps over the lazy dog")
print(result)
# {'lang': 'en', 'score': 0.97...}

Only completely empty or whitespace-only input raises ValueError (since there's nothing to detect).

Detecting multiple languages (bilingual / code-switched text)

Pass k=N (where N > 1) to get the top-N candidate languages, sorted by descending score. This is useful for bilingual sentences, mixed-language paragraphs, or whenever you want to see runner-up predictions. The default (k=1) is unchanged and still returns a single dict.

from ftlangdetect import detect

text = "The quick brown fox. Le chat dort sur le canapé."
results = detect(text=text, low_memory=False, k=3)
print(results)
# [
#   {'lang': 'fr', 'score': 0.71},
#   {'lang': 'en', 'score': 0.27},
#   {'lang': 'de', 'score': 0.005},
# ]

`k` value	Return type
`1` (default)	`DetectionResult` (`{'lang': str, 'score': float}`)
`> 1`	`list[DetectionResult]`, length up to `k`, sorted by score desc

Model cache location

The model is downloaded on first use and cached on disk. By default the cache lives in the system temp directory under fasttext-langdetect/. Set the FTLANG_CACHE environment variable to override the location:

export FTLANG_CACHE=~/.cache/fasttext-langdetect

If a cached model fails to load (for example a corrupt file left over from a much older release), the library will now delete it and re-download it once automatically. As a manual fallback you can always clear the cache by hand:

rm -rf "${FTLANG_CACHE:-/tmp/fasttext-langdetect}"

Development

git clone https://github.com/zafercavdar/fasttext-langdetect.git
cd fasttext-langdetect
python -m pip install -e ".[dev]"
pre-commit install

make check   # ruff lint + format check
make test    # pytest
make cov     # pytest with coverage
make build   # build sdist + wheel

This project uses ruff for linting and formatting, pytest for tests, hatchling as the build backend, and pre-commit for git hooks.

Benchmark

We benchmarked the fasttext model against cld2, langid, and langdetect on Wili-2018 dataset.

	fasttext	langid	langdetect	cld2
Average time (ms)	0,158273381	1,726618705	12,44604317	0,028776978
139 langs - not weighted	76,8	61,6	37,6	80,8
139 langs - pop weighted	95,5	93,1	86,6	92,7
44 langs - not weighted	93,3	89,2	81,6	91,5
44 langs - pop weighted	96,6	94,8	89,4	93,4

pop weighted means recall for each language is multipled by its number of speakers.
139 languages = all languages with ISO 639-1 2-letter code
44 languages = top 44 languages spoken in the world

Recall per language

lang	cld2	fasttext	langdetect	langid
Afrikaans	0,94	0,918	0,992	0,966
Albanian	0,958	0,966	0,964	0,954
Amharic	0,976	0,982	0	0,982
Arabic	0,994	0,998	0,998	0,996
Aragonese	0	0,43	0	0,788
Armenian	0,966	0,972	0	0,968
Assamese	0,946	0,956	0	0,14
Avar	0	0,626	0	0
Aymara	0,596	0	0	0
Azerbaijani	0,97	0,988	0	0,984
Bashkir	0,97	0,97	0	0
Basque	0,978	0,99	0	0,962
Belarusian	0,94	0,97	0	0,964
Bengali	0,898	0,922	0,904	0,942
Bhojpuri	0,716	0,15	0	0
Bokmål	0,852	0,966	0,976	0,95
Bosnian	0,422	0,108	0	0,054
Breton	0,946	0,974	0	0,976
Bulgarian	0,892	0,964	0,964	0,942
Burmese	0,998	0,998	0	0
Catalan	0,882	0,95	0,93	0,928
Central Khmer	0,876	0,878	0	0,876
Chechen	0	0,99	0	0
Chuvash	0	0,96	0	0
Cornish	0	0,792	0	0
Corsican	0,88	0,016	0	0
Croatian	0,688	0,806	0,982	0,932
Czech	0,978	0,986	0,984	0,982
Danish	0,886	0,958	0,95	0,896
Dhivehi	0,996	0,998	0	0
Dutch	0,9	0,978	0,968	0,97
English	0,992	1	0,998	0,986
Esperanto	0,936	0,978	0	0,948
Estonian	0,918	0,952	0,948	0,932
Faroese	0,912	0	0	0,618
Finnish	0,988	0,998	0,998	0,994
French	0,946	0,996	0,99	0,992
Galician	0,89	0,912	0	0,93
Georgian	0,974	0,976	0	0,976
German	0,958	0,984	0,978	0,978
Guarani	0,968	0,728	0	0
Gujarati	0,932	0,932	0,93	0,932
Haitian Creole	0,988	0,536	0	0,99
Hausa	0,976	0	0	0
Hebrew	0,994	0,996	0,998	0,998
Hindi	0,982	0,984	0,982	0,972
Hungarian	0,96	0,988	0,968	0,986
Icelandic	0,984	0,996	0	0,996
Ido	0	0,76	0	0
Igbo	0,798	0	0	0
Indonesian	0,88	0,946	0,958	0,836
Interlingua	0,27	0,688	0	0
Interlingue	0,198	0,192	0	0
Irish	0,968	0,978	0	0,984
Italian	0,866	0,948	0,932	0,936
Japanese	0,97	0,986	0,98	0,986
Javanese	0	0,864	0	0,938
Kannada	0,998	0,998	0,998	0,998
Kazakh	0,978	0,992	0	0,916
Kinyarwanda	0,86	0	0	0,44
Kirghiz	0,974	0,99	0	0,408
Komi	0	0,544	0	0
Korean	0,986	0,99	0,988	0,99
Kurdish	0	0,972	0	0,976
Lao	0,84	0,842	0	0,85
Latin	0,778	0,864	0	0,854
Latvian	0,98	0,992	0,992	0,99
Limburgan	0	0,324	0	0
Lingala	0,85	0	0	0
Lithuanian	0,96	0,976	0,974	0,97
Luganda	0,952	0	0	0
Luxembourgish	0,864	0,894	0	0,93
Macedonian	0,88	0,984	0,982	0,974
Malagasy	0,99	0,99	0	0,988
Malay	0,896	0,586	0	0,39
Malayalam	0,988	0,988	0,988	0,988
Maltese	0,962	0,966	0	0,964
Manx	0,972	0,294	0	0
Maori	0,994	0	0	0
Marathi	0,958	0,966	0,964	0,942
Modern Greek	0,99	0,992	0,99	0,992
Mongolian	0,964	0,994	0	0,996
Navajo	0	0	0	0
Nepali (macrolanguage)	0,96	0,98	0,978	0,922
Northern Sami	0	0	0	0,866
Norwegian Nynorsk	0,94	0,79	0	0,796
Occitan	0,66	0,48	0	0,724
Oriya	0,96	0,958	0	0,96
Oromo	0,956	0	0	0
Ossetian	0	0,938	0	0
Panjabi	0,994	0,994	0,994	0,994
Persian	0,992	0,998	0,996	0,998
Polish	0,982	0,998	0,998	0,992
Portuguese	0,908	0,956	0,946	0,952
Pushto	0,938	0,922	0	0,754
Quechua	0,926	0,808	0	0,852
Romanian	0,932	0,986	0,984	0,984
Romansh	0,934	0,328	0	0
Russian	0,728	0,986	0,984	0,988
Sanskrit	0,964	0,976	0	0
Sardinian	0	0,01	0	0
Scottish Gaelic	0,964	0,942	0	0
Serbian	0,942	0,946	0	0,902
Serbo-Croatian	0	0,402	0	0
Shona	0,844	0	0	0
Sindhi	0,978	0,982	0	0
Sinhala	0,962	0,962	0	0,962
Slovak	0,964	0,974	0,982	0,97
Slovene	0,876	0,966	0,968	0,946
Somali	0,924	0,696	0,956	0
Spanish	0,894	0,986	0,976	0,98
Standard Chinese	0,946	0,984	0,746	0,978
Sundanese	0,91	0,854	0	0
Swahili (macrolanguage)	0,924	0,92	0,938	0,934
Swedish	0,872	0,994	0,992	0,986
Tagalog	0,928	0,972	0,974	0,964
Tajik	0,82	0,85	0	0
Tamil	0,992	0,992	0,992	0,994
Tatar	0,978	0,984	0	0
Telugu	0,958	0,958	0,958	0,96
Thai	0,988	0,988	0,988	0,988
Tibetan	0,986	0,992	0	0
Tongan	0,968	0	0	0
Tswana	0,928	0	0	0
Turkish	0,968	0,986	0,982	0,976
Turkmen	0,94	0,936	0	0
Uighur	0,978	0,986	0	0,964
Ukrainian	0,97	0,988	0,986	0,986
Urdu	0,86	0,958	0,89	0,896
Uzbek	0,984	0,99	0	0
Vietnamese	0,978	0,986	0,984	0,984
Volapük	0,994	0,982	0	0,986
Walloon	0	0,664	0	0,98
Welsh	0,98	0,992	0,992	0,984
Western Frisian	0,888	0,956	0	0
Wolof	0,926	0	0	0
Xhosa	0,928	0	0	0,912
Yiddish	0,956	0,958	0	0
Yoruba	0,75	0,262	0	0

Star History

References

[1] A. Joulin, E. Grave, P. Bojanowski, T. Mikolov, Bag of Tricks for Efficient Text Classification

@article{joulin2016bag,
  title={Bag of Tricks for Efficient Text Classification},
  author={Joulin, Armand and Grave, Edouard and Bojanowski, Piotr and Mikolov, Tomas},
  journal={arXiv preprint arXiv:1607.01759},
  year={2016}
}

[2] A. Joulin, E. Grave, P. Bojanowski, M. Douze, H. Jégou, T. Mikolov, FastText.zip: Compressing text classification models

@article{joulin2016fasttext,
  title={FastText.zip: Compressing text classification models},
  author={Joulin, Armand and Grave, Edouard and Bojanowski, Piotr and Douze, Matthijs and J{\'e}gou, H{\'e}rve and Mikolov, Tomas},
  journal={arXiv preprint arXiv:1612.03651},
  year={2016}
}