fix: preserve plural number placeholder tag during machine translation

[braindeaf]

Observed bug

When create a new set of keys for a Rails application, we push tolgee push and we get an auto-translation of values for all the languages we support.

    with_attachments:
      one: "%{count} file uploaded:"
      other: "%{count} files uploaded:"

However it is not uncommon for the %{count} within the auto-translated text to be # or #{count} or even %'{'count'}' which indicates an issue with preserving these interpolation placeholders.

Summary

When auto-translating a plural key through a machine translation provider that doesn't support ICU plurals natively (Google, DeepL, Azure, AWS — everything except the LLM/prompt-based provider), each plural form is translated in a separate request. To protect the ICU # (replace-number) placeholder during that request, PluralTranslationUtil substitutes a real example number wrapped in a <x id="tolgee-number"> tag before sending the text to the provider, then strips the tag back to # afterward.

The bug: none of the provider API calls actually told the engine to preserve that tag. Each provider was free to translate through it, reposition it, or drop it entirely — so restoration of # was unreliable. In practice this surfaces as things like Ruby/Rails %{count} coming back as #{count}, a bare #, or an escaped literal placeholder after re-export, essentially every time a plural key went through auto-translate with one of these providers.

Fix

• Added a containsNumberTag flag that flows from PluralTranslationUtil through TranslationParams / ProviderTranslateParams to each provider.
• Each provider now opts into its own documented tag-preserving/HTML mode when the flag is set:
  • DeepL: tag_handling=xml + ignore_tags=x
  • Azure: textType=html
  • Google: format("html") instead of the hardcoded "text"
  • AWS: contentType("text/html"), which is required for its existing translate="no" span wrapping (HtmlNoTranslatePlaceholderProtector) to actually take effect
• Baidu is unchanged — its basic translate API doesn't document a tag-exclusion mechanism.
• Updated the two existing tests whose mocks needed a matcher for the new parameter (DeeplTranslationProviderTest, TranslationSuggestionControllerMtTest).

Test plan

• ./gradlew :data:test --tests "*Deepl*" --tests "*PluralTranslationUtil*"
• ./gradlew :app:test --tests "*TranslationSuggestionControllerMtTest*"
• Manual: auto-translate a plural key (e.g. Rails-style one/other with %{count}) through DeepL, Google, Azure, and AWS, and confirm the exported translation keeps %{count} (or the target format's equivalent) intact for both forms.

Note: I wasn't able to compile/run the test suite locally (this environment only had a Java 26 toolchain available; the project pins Java 25 and toolchain auto-provisioning isn't configured here), so please treat CI as the first real build of this change.

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Summary by CodeRabbit

• Bug Fixes
  • Improved machine translation handling for pluralized text containing protected number placeholders.
  • Translation providers now preserve these placeholders across supported services, reducing the risk of corrupted or altered plural formatting.
  • Provider-specific formatting is automatically selected when protected tags are present, while standard text handling remains unchanged.

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• backend/data/src/test/kotlin/io/tolgee/unit/component/machineTranslation/DeeplTranslationProviderTest.kt

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📝 Walkthrough

Walkthrough

Machine translation now detects plural number tags, propagates the flag through translation parameters, and enables tag-preserving modes for Azure, DeepL, and Google. Cache keys include the flag, and tests verify updated provider calls.

Changes

Number-tag preservation

Layer / File(s)	Summary
Number-tag metadata propagation backend/data/src/main/kotlin/io/tolgee/service/machineTranslation/PluralTranslationUtil.kt, backend/data/src/main/kotlin/io/tolgee/service/machineTranslation/MtBatchTranslator.kt, backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/...	The translation flow detects number tags, forwards the flag to provider parameters, and includes it in cache keys.
Provider request mode selection backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/providers/...	Azure uses HTML mode, DeepL uses XML tag handling, and Google uses HTML format when the input contains a number tag.
Provider API compatibility validation backend/data/src/test/kotlin/io/tolgee/unit/component/machineTranslation/DeeplTranslationProviderTest.kt, backend/app/src/test/kotlin/io/tolgee/api/v2/controllers/translationSuggestionController/TranslationSuggestionControllerMtTest.kt	Tests verify DeepL tag handling and update mocks for the expanded provider method signatures.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 51828

This change preserves plural number placeholders during machine translation by selecting provider formats that retain the protected tag. The implementation is ready to merge with no identified current production risk.

Sequence Diagram(s)

sequenceDiagram
  participant MtBatchTranslator
  participant PluralTranslationUtil
  participant MtServiceManager
  participant TranslationProvider
  participant TranslationAPI
  MtBatchTranslator->>PluralTranslationUtil: Detect number tag
  PluralTranslationUtil-->>MtBatchTranslator: containsNumberTag flag
  MtBatchTranslator->>MtServiceManager: Build TranslationParams
  MtServiceManager->>TranslationProvider: Pass ProviderTranslateParams
  TranslationProvider->>TranslationAPI: Request HTML or XML tag-preserving mode
  TranslationAPI-->>TranslationProvider: Return translated text with protected tags

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❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 7.69% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 13 functions across 13 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

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Check name	Status	Explanation
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Title check	✅ Passed	The title clearly and concisely describes the main change: preserving plural number placeholder tags during machine translation.
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Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Inline comments:
In
`@backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/providers/AwsMtValueProvider.kt`:
- Line 49: Remove the unsupported contentType call from the TranslateTextRequest
builder in AwsMtValueProvider, leaving the existing request construction and
translation behavior unchanged.

In
`@backend/data/src/test/kotlin/io/tolgee/unit/component/machineTranslation/DeeplTranslationProviderTest.kt`:
- Line 49: Update the relevant DeeplTranslationProvider test to exercise the
containsNumberTag=true path by setting that input to true and expecting
eq(true), or add a separate test covering XML mode while retaining the existing
preserveTags=false coverage.

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📥 Commits

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📒 Files selected for processing (13)

• backend/app/src/test/kotlin/io/tolgee/api/v2/controllers/translationSuggestionController/TranslationSuggestionControllerMtTest.kt
• backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/MtServiceManager.kt
• backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/TranslationParams.kt
• backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/providers/AwsMtValueProvider.kt
• backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/providers/AzureCognitiveApiService.kt
• backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/providers/AzureCognitiveTranslationProvider.kt
• backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/providers/DeeplApiService.kt
• backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/providers/DeeplTranslationProvider.kt
• backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/providers/GoogleTranslationProvider.kt
• backend/data/src/main/kotlin/io/tolgee/component/machineTranslation/providers/ProviderTranslateParams.kt
• backend/data/src/main/kotlin/io/tolgee/service/machineTranslation/MtBatchTranslator.kt
• backend/data/src/main/kotlin/io/tolgee/service/machineTranslation/PluralTranslationUtil.kt
• backend/data/src/test/kotlin/io/tolgee/unit/component/machineTranslation/DeeplTranslationProviderTest.kt

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