From 4614931ae17c2407495571db44c765f66e66a929 Mon Sep 17 00:00:00 2001
From: Virgil <virgil@lethean.io>
Date: Thu, 2 Apr 2026 06:26:29 +0000
Subject: [PATCH] fix(i18n): prefer locale override precedence

Co-Authored-By: Virgil <virgil@lethean.io>
---
 localise.go      | 32 +++++++++++++++++---------------
 localise_test.go | 30 ++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 15 deletions(-)

diff --git a/localise.go b/localise.go
index d4ad110..ac481a3 100644
--- a/localise.go
+++ b/localise.go
@@ -114,33 +114,35 @@ func CurrentPluralCategory(n int) PluralCategory {
 }
 
 func detectLanguage(supported []language.Tag) string {
-	langEnv := os.Getenv("LANG")
-	if langEnv == "" {
-		langEnv = os.Getenv("LC_ALL")
+	for _, langEnv := range []string{os.Getenv("LC_ALL"), os.Getenv("LC_MESSAGES"), os.Getenv("LANG")} {
 		if langEnv == "" {
-			langEnv = os.Getenv("LC_MESSAGES")
+			continue
+		}
+		if detected := detectLanguageFromEnv(langEnv, supported); detected != "" {
+			return detected
 		}
 	}
-	if langEnv == "" {
+	return ""
+}
+
+func detectLanguageFromEnv(langEnv string, supported []language.Tag) string {
+	baseLang := normalizeLanguageTag(core.Split(langEnv, ".")[0])
+	if baseLang == "" || len(supported) == 0 {
 		return ""
 	}
-	baseLang := normalizeLanguageTag(core.Split(langEnv, ".")[0])
 	parsedLang, err := language.Parse(baseLang)
 	if err != nil {
 		return ""
 	}
-	if len(supported) == 0 {
-		return ""
-	}
 	matcher := language.NewMatcher(supported)
 	bestMatch, bestIndex, confidence := matcher.Match(parsedLang)
-	if confidence >= language.Low {
-		if bestIndex >= 0 && bestIndex < len(supported) {
-			return supported[bestIndex].String()
-		}
-		return bestMatch.String()
+	if confidence < language.Low {
+		return ""
 	}
-	return ""
+	if bestIndex >= 0 && bestIndex < len(supported) {
+		return supported[bestIndex].String()
+	}
+	return bestMatch.String()
 }
 
 func normalizeLanguageTag(lang string) string {
diff --git a/localise_test.go b/localise_test.go
index ced2a26..3bcc640 100644
--- a/localise_test.go
+++ b/localise_test.go
@@ -5,6 +5,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"golang.org/x/text/language"
 )
 
 // --- Formality.String() ---
@@ -249,6 +250,35 @@ func TestDetectLanguage_Good(t *testing.T) {
 	assert.Equal(t, "", result, "should return empty with no supported languages")
 }
 
+func TestDetectLanguage_PrefersLocaleOverrides(t *testing.T) {
+	t.Setenv("LANG", "en_US.UTF-8")
+	t.Setenv("LC_MESSAGES", "fr_FR.UTF-8")
+	t.Setenv("LC_ALL", "de_DE.UTF-8")
+
+	supported := []language.Tag{
+		language.AmericanEnglish,
+		language.French,
+		language.German,
+	}
+
+	result := detectLanguage(supported)
+	assert.Equal(t, "de", result, "LC_ALL should win over LANG and LC_MESSAGES")
+}
+
+func TestDetectLanguage_SkipsInvalidHigherPriorityLocale(t *testing.T) {
+	t.Setenv("LANG", "en_US.UTF-8")
+	t.Setenv("LC_MESSAGES", "fr_FR.UTF-8")
+	t.Setenv("LC_ALL", "not-a-locale")
+
+	supported := []language.Tag{
+		language.AmericanEnglish,
+		language.French,
+	}
+
+	result := detectLanguage(supported)
+	assert.Equal(t, "fr", result, "invalid LC_ALL should not block a valid lower-priority locale")
+}
+
 // --- Mode.String() ---
 
 func TestMode_String_Good(t *testing.T) {
-- 
2.45.3