fix(transcription): honor model-config language/translate + OpenAI language form field (#10731)

fix(transcription): honor model-config language/translate, add language form field

The /v1/audio/transcriptions endpoint read only input.Language /
input.Translate from the parsed request, and the request middleware never
populates those from a multipart upload -- nor did it read a `language`
form field. As a result the model config's parameters.language /
parameters.translate (a valid PredictionOptions field under `parameters:`)
were silently ignored, and multilingual models like canary defaulted to
translating into English even when the YAML set language: ru,
translate: false (#10655).

Resolve both with clear precedence: the request form field wins, then any
language on the parsed request, then the model config default. This also
makes the endpoint honor OpenAI's `language` form parameter, which was
not read before.

Applies to both the streaming and non-streaming paths (the resolved
values are built into the shared TranscriptionRequest). Note this ensures
the language/translate flags reach the backend; whether a given engine
acts on them is up to the backend.

Closes #10655


Assisted-by: Claude:claude-opus-4-8 [Claude Code]

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

core/http/endpoints/openai/transcription.go

@@ -33,6 +33,29 @@ import (
 // @Param stream formData boolean false "stream partial results as SSE"
 // @Success 200 {object} map[string]string	 "Response"
 // @Router /v1/audio/transcriptions [post]
+// resolveTranscriptionLanguage picks the transcription language. The request
+// form field (OpenAI's `language` param) wins, then any language carried on the
+// parsed request, and finally the model config default (parameters.language).
+func resolveTranscriptionLanguage(formLanguage, requestLanguage, configLanguage string) string {
+	if formLanguage != "" {
+		return formLanguage
+	}
+	if requestLanguage != "" {
+		return requestLanguage
+	}
+	return configLanguage
+}
+
+// resolveTranscriptionTranslate picks the translate flag: the request form
+// field (`translate`, when a valid bool) wins over the model config default
+// (parameters.translate).
+func resolveTranscriptionTranslate(formTranslate string, configTranslate bool) bool {
+	if b, err := strconv.ParseBool(formTranslate); err == nil {
+		return b
+	}
+	return configTranslate
+}
+
 func TranscriptEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, appConfig *config.ApplicationConfig) echo.HandlerFunc {
 	return func(c echo.Context) error {
 		input, ok := c.Get(middleware.CONTEXT_LOCALS_KEY_LOCALAI_REQUEST).(*schema.OpenAIRequest)
@@ -112,10 +135,19 @@ func TranscriptEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, app
 
 		xlog.Debug("Audio file copied", "dst", dst)
 
+		// Language/translate resolve with the request form field taking
+		// precedence over the model config default (parameters.language /
+		// parameters.translate). Previously only the parsed request was read,
+		// which for a multipart upload never carries these, so config-level
+		// settings were silently ignored and multilingual models (e.g. canary)
+		// defaulted to English translation. (#10655)
+		language := resolveTranscriptionLanguage(c.FormValue("language"), input.Language, config.Language)
+		translate := resolveTranscriptionTranslate(c.FormValue("translate"), config.Translate)
+
 		req := backend.TranscriptionRequest{
 			Audio:                  dst,
-			Language:               input.Language,
-			Translate:              input.Translate,
+			Language:               language,
+			Translate:              translate,
 			Diarize:                diarize,
 			Prompt:                 prompt,
 			Temperature:            temperature,

core/http/endpoints/openai/transcription_resolve_test.go

@@ -0,0 +1,48 @@
+package openai
+
+import (
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Transcription language/translate resolution", func() {
+	Describe("resolveTranscriptionLanguage", func() {
+		It("prefers the request form field over everything", func() {
+			Expect(resolveTranscriptionLanguage("en", "fr", "ru")).To(Equal("en"))
+		})
+
+		It("falls back to the parsed request when the form field is empty", func() {
+			Expect(resolveTranscriptionLanguage("", "fr", "ru")).To(Equal("fr"))
+		})
+
+		It("falls back to the model config default when nothing else is set", func() {
+			// The reporter set parameters.language: ru in the model YAML but sent
+			// no language form field; the config value must be honored. (#10655)
+			Expect(resolveTranscriptionLanguage("", "", "ru")).To(Equal("ru"))
+		})
+
+		It("returns empty when no source provides a language", func() {
+			Expect(resolveTranscriptionLanguage("", "", "")).To(Equal(""))
+		})
+	})
+
+	Describe("resolveTranscriptionTranslate", func() {
+		It("honors a request form field of true", func() {
+			Expect(resolveTranscriptionTranslate("true", false)).To(BeTrue())
+		})
+
+		It("honors a request form field of false over a config default of true", func() {
+			Expect(resolveTranscriptionTranslate("false", true)).To(BeFalse())
+		})
+
+		It("falls back to the model config default when the form field is absent", func() {
+			// parameters.translate: true in the YAML must be honored when no form
+			// field overrides it.
+			Expect(resolveTranscriptionTranslate("", true)).To(BeTrue())
+		})
+
+		It("defaults to the config value (false) when neither is set", func() {
+			Expect(resolveTranscriptionTranslate("", false)).To(BeFalse())
+		})
+	})
+})