feat(machinery): add Argos offline translation backend by knk125 · Pull Request #18572 · WeblateOrg/weblate

knk125 · 2026-03-22T16:18:00Z

Add Argos Translate Offline Machine Translation Backend (issiue: #13106)
Description
This Pull Request introduces a new offline machine translation backend utilizing Argos Translate.

Argos Translate is an open-source offline translation library written in Python. It is based on OpenNMT (Open Neural Machine Translation) and runs inference locally using CTranslate2, providing high-quality translations without relying on third-party external APIs, thereby ensuring complete data privacy.

Implementation Details
Dependency Addition: Added argostranslate as an optional Python dependency under the [all] and [argos] extras in
pyproject.toml
.
Backend Engine: Created
weblate/machinery/argos.py
, which implements the
ArgosTranslation
class extending the base
MachineTranslation
engine.
The engine leverages argostranslate.translate.get_installed_languages() to dynamically determine which language pairs are locally supported via the
is_supported
method.
The
download_translations
method handles querying the local CTranslate2 models synchronously and yielding structured translation suggestions.
Registration: Registered "weblate.machinery.argos.ArgosTranslation" into the WEBLATE_MACHINERY tuple in
weblate/machinery/models.py
.
Testing methodology
Initialized a component inside a local Weblate instance and explicitly enabled the Argos Translate service within the project's machinery_settings config.
Installed the English-Spanish Argos model via Python bindings.
Passed a mock English source string unit to the API endpoint and received accurate translations on the Weblate UI under the "Automatic suggestions" tab.
No external cloud API keys are required for this engine to function since inference executes entirely on the local device's CPU/GPU.

nijel · 2026-03-22T19:19:43Z

Can you please add tests?

Copilot

Pull request overview

Adds a new offline machine translation backend based on Argos Translate, integrating it into Weblate’s machinery registry and packaging extras so it can be enabled as a service.

Changes:

Added ArgosTranslation machinery backend (weblate/machinery/argos.py) using argostranslate installed models.
Registered the backend in WEBLATE_MACHINERY so it’s discoverable/configurable.
Added an argos optional dependency extra and included it in the all extra.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
`weblate/machinery/models.py`	Registers the new machinery class so it can be loaded by the machinery class loader.
`weblate/machinery/argos.py`	Implements Argos Translate-backed offline translation and language-pair support checks.
`pyproject.toml`	Adds `argostranslate` as an optional dependency and wires it into the `all` extra.

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nijel

Thanks for your contribution. Besides the previous comments, this has CI failures and lacks documentation. make -C docs update-docs will bring you the basic backend documentation generated from the code (this should be documented and we will fix that, see #18724).

nijel · 2026-03-30T14:20:58Z

+        src = source_language.split("-")[0].lower()
+        tgt = target_language.split("-")[0].lower()
+
+        installed_languages = argostranslate.translate.get_installed_languages()


How is language installation supposed to work?

nijel · 2026-03-30T14:24:14Z

PS: What I find super confusing is that we're using Argos CI for screenshot testing, and this brings another thing named Argos just in an absolutely different scope. But this is nothing we can address.

codecov · 2026-03-30T14:28:34Z

⚠️ JUnit XML file not found

The CLI was unable to find any JUnit XML files to upload.
For more help, visit our troubleshooting guide.

Co-authored-by: Michal Čihař <michal@cihar.com>

for more information, see https://pre-commit.ci

Copilot

Pull request overview

Copilot reviewed 4 out of 5 changed files in this pull request and generated 5 comments.

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Copilot · 2026-04-01T06:34:40Z

+from typing import TYPE_CHECKING
+
+import argostranslate.translate
+
+from .base import MachineTranslation


argostranslate is imported at module import time, which will raise ImportError when the optional dependency isn’t installed. Because this backend is listed in WEBLATE_MACHINERY, an ImportError here will prevent the ClassLoader from loading the service cleanly (and can break commands/UI that enumerate machinery). Make the import optional (e.g., try/except) and set is_available based on whether argostranslate is importable, or defer the import into methods.

Copilot · 2026-04-01T06:34:40Z

+        src = source_language.split("-")[0].lower()
+        tgt = target_language.split("-")[0].lower()
+
+        installed_languages = argostranslate.translate.get_installed_languages()
+
+        src_lang = next(
+            (lang for lang in installed_languages if lang.code == src), None
+        )
+        tgt_lang = next(
+            (lang for lang in installed_languages if lang.code == tgt), None
+        )
+
+        if src_lang and tgt_lang:
+            return src_lang.get_translation(tgt_lang) is not None
+


is_supported() calls argostranslate.translate.get_installed_languages() on every support check. This method is called repeatedly during language negotiation, so it’s worth caching the installed languages (or a src→targets map) on the instance (e.g., via @cached_property) to avoid repeated scanning/work.

Copilot · 2026-04-01T06:34:40Z

+        except Exception as e:
+            logger.debug(
+                "Argos translation failed for %s to %s: %s",
+                source_language,
+                target_language,
+                e,


The exception handler logs only the exception string, which loses traceback context for debugging. Consider logging with exc_info=True (or using logger.exception at debug level) so failures in local model execution are diagnosable.

Suggested change

except Exception as e:

logger.debug(

"Argos translation failed for %s to %s: %s",

source_language,

target_language,

e,

except Exception:

logger.debug(

"Argos translation failed for %s to %s",

source_language,

target_language,

exc_info=True,

Copilot · 2026-04-01T06:34:40Z

+class ArgosTranslationTest(BaseMachineTranslationTest):
+    MACHINE_CLS = ArgosTranslation
+    EXPECTED_LEN = 1
+
+    def mock_empty(self) -> None:
+        self.skipTest("Not tested")
+
+    def mock_error(self) -> None:
+        self.skipTest("Not tested")
+
+    def mock_response(self) -> None:
+        pass
+
+    @patch("weblate.machinery.argos.ArgosTranslation.is_available", True)
+    @patch("weblate.machinery.argos.argostranslate")
+    def test_translate(self, mock_argostranslate, **kwargs) -> None:
+        mock_lang_en = MagicMock()


This test class inherits BaseMachineTranslationTest.test_validate_settings(), which will call machine.validate_settings() without any patching. In CI, workflows install with --all-extras, so argostranslate will likely be present and validate_settings() will call the real Argos runtime (and likely fail unless models are installed). Override test_validate_settings() (or mock_response()) here to patch weblate.machinery.argos.argostranslate similarly to the other tests, or explicitly skip the validation test for this backend.

Copilot · 2026-04-01T06:34:41Z

+  "weblate[alibaba,amazon,argos,gerrit,gelf,google,ldap,mercurial,openai,postgres,sphinx,zxcvbn]"
 ]
 amazon = [
  "boto3>=1.38.0,<2.0"
 ]
+argos = [
+  "argostranslate"


The new argos extra is unpinned (argostranslate without a version range), while most other optional deps are constrained. Add an upper bound (and ideally a minimum known-good version) to reduce breakage risk from upstream releases. Also note that adding argos to the all extra will pull in very large transitive deps (e.g., torch/spacy/stanza), which can significantly impact install time/CI resource usage (workflows use uv sync --all-extras).

Suggested change

"weblate[alibaba,amazon,argos,gerrit,gelf,google,ldap,mercurial,openai,postgres,sphinx,zxcvbn]"

]

amazon = [

"boto3>=1.38.0,<2.0"

]

argos = [

"argostranslate"

"weblate[alibaba,amazon,gerrit,gelf,google,ldap,mercurial,openai,postgres,sphinx,zxcvbn]"

]

amazon = [

"boto3>=1.38.0,<2.0"

]

argos = [

"argostranslate>=1.9.0,<2.0.0"

feat(machinery): add Argos offline translation backend

01799ea

knk125 requested a review from nijel as a code owner March 22, 2026 16:18

nijel requested a review from Copilot March 22, 2026 19:19

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Comment thread pyproject.toml

Comment thread weblate/machinery/argos.py

Comment thread weblate/machinery/argos.py Outdated

Comment thread weblate/machinery/argos.py

Comment thread weblate/machinery/argos.py

nijel reviewed Mar 24, 2026

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Comment thread weblate/machinery/argos.py Outdated

Update Argos machinery and tests

1954957

knk125 force-pushed the feature/argos-translation branch from a9deab0 to 1954957 Compare March 26, 2026 15:46

pre-commit-ci Bot and others added 6 commits March 26, 2026 15:48

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Merge branch 'main' into feature/argos-translation

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Merge branch 'main' into feature/argos-translation

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Merge branch 'main' into feature/argos-translation

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Merge branch 'main' into feature/argos-translation

c3d3898

nijel reviewed Mar 30, 2026

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chore(pre-commit): apply code formatting

de2715d

knk125 and others added 4 commits March 30, 2026 17:28

Merge branch 'main' into feature/argos-translation

650945d

Update weblate/machinery/argos.py

3cfd49c

Co-authored-by: Michal Čihař <michal@cihar.com>

Update weblate/machinery/argos.py

ed3881b

Co-authored-by: Michal Čihař <michal@cihar.com>

[pre-commit.ci] auto fixes from pre-commit.com hooks

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nijel requested a review from Copilot April 1, 2026 06:27

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codecov Bot commented Mar 30, 2026

⚠️ JUnit XML file not found

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knk125 commented Mar 22, 2026 •

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