fix: case-insensitive locale tag comparison in resolveLocale

Locale tags with region or script (e.g. zh-Hans, pt-BR) failed to match
because Locale.equals() compares fields case-sensitively. Use lowercase
tag-based lookup instead, preserving the original locale casing for CDN
file paths.

Closes #12

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Anty0

core/build.gradle.kts

@@ -216,6 +216,10 @@ kotlin {
             implementation(libs.coroutines)
         }
 
+        commonTest.dependencies {
+            implementation(kotlin("test"))
+        }
+
         androidMain.dependencies {
             implementation(libs.android)
 

core/src/commonMain/kotlin/io/tolgee/Tolgee.kt

@@ -236,13 +236,19 @@ open class Tolgee(
             return locale
         }
 
+        // Build a map keyed by lowercase tag for case-insensitive matching.
+        // Returns the original available locale to preserve the exact casing
+        // needed for CDN file paths.
+        val localesByTag = availableLocales.associateBy { it.toTag("-").lowercase() }
+
         // Generate progressive fallback variations
         val fallbackCandidates = generateLocaleFallbacks(locale)
 
-        // Try each fallback candidate in order
+        // Try each fallback candidate in order (case-insensitive)
         for (candidate in fallbackCandidates) {
-            if (candidate in availableLocales) {
-                return candidate
+            val matchedLocale = localesByTag[candidate.toTag("-").lowercase()]
+            if (matchedLocale != null) {
+                return matchedLocale
             }
         }
 
@@ -457,7 +463,8 @@ open class Tolgee(
                 ?: emptyList()
 
             val currentLocale = resolveLocale(localeFlow.value)
-            val otherLocales = availableLocales.filter { it != currentLocale }
+            val currentLocaleTag = currentLocale?.toTag("-")?.lowercase()
+            val otherLocales = availableLocales.filter { it.toTag("-").lowercase() != currentLocaleTag }
 
             otherLocales.forEach { locale ->
                 suspendCatching {

core/src/commonTest/kotlin/io/tolgee/ResolveLocaleTest.kt

@@ -0,0 +1,90 @@
+package io.tolgee
+
+import de.comahe.i18n4k.Locale
+import de.comahe.i18n4k.forLocaleTag
+import de.comahe.i18n4k.toTag
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+class ResolveLocaleTest {
+
+    /**
+     * Testable subclass that exposes resolveLocale for testing.
+     */
+    private class TestableTolgee(config: Tolgee.Config) : Tolgee(config) {
+        fun testResolveLocale(locale: Locale?): Locale? = resolveLocale(locale)
+    }
+
+    private fun createTolgee(
+        availableLocales: List<Locale>,
+        defaultLanguage: Locale? = null,
+    ): TestableTolgee {
+        val config = Tolgee.Config.Builder()
+            .availableLocales(availableLocales)
+            .apply { defaultLanguage?.let { defaultLanguage(it) } }
+            .build()
+        return TestableTolgee(config)
+    }
+
+    @Test
+    fun exactMatchWorks() {
+        val tolgee = createTolgee(listOf(forLocaleTag("en"), forLocaleTag("zh-Hans")))
+        val result = tolgee.testResolveLocale(forLocaleTag("zh-Hans"))
+        assertEquals("zh-Hans", result?.toTag("-"))
+    }
+
+    @Test
+    fun caseInsensitiveMatchForScript() {
+        val tolgee = createTolgee(listOf(forLocaleTag("en"), forLocaleTag("zh-Hans")))
+        val result = tolgee.testResolveLocale(forLocaleTag("zh-hans"))
+        assertEquals("zh-Hans", result?.toTag("-"))
+    }
+
+    @Test
+    fun caseInsensitiveMatchForRegion() {
+        val tolgee = createTolgee(listOf(forLocaleTag("en"), forLocaleTag("pt-BR")))
+        val result = tolgee.testResolveLocale(forLocaleTag("pt-br"))
+        assertEquals("pt-BR", result?.toTag("-"))
+    }
+
+    @Test
+    fun fallbackFromRegionToBaseLanguage() {
+        val tolgee = createTolgee(listOf(forLocaleTag("en"), forLocaleTag("pt")))
+        val result = tolgee.testResolveLocale(forLocaleTag("pt-BR"))
+        assertEquals("pt", result?.toTag("-"))
+    }
+
+    @Test
+    fun fallbackFromScriptRegionToScript() {
+        val tolgee = createTolgee(listOf(forLocaleTag("en"), forLocaleTag("zh-Hans")))
+        val result = tolgee.testResolveLocale(forLocaleTag("zh-Hans-CN"))
+        assertEquals("zh-Hans", result?.toTag("-"))
+    }
+
+    @Test
+    fun fallsBackToDefaultLanguageWhenNoMatch() {
+        val defaultLang = forLocaleTag("en")
+        val tolgee = createTolgee(
+            listOf(forLocaleTag("en"), forLocaleTag("fr")),
+            defaultLanguage = defaultLang,
+        )
+        val result = tolgee.testResolveLocale(forLocaleTag("ja"))
+        assertEquals("en", result?.toTag("-"))
+    }
+
+    @Test
+    fun nullLocaleReturnsNull() {
+        val tolgee = createTolgee(listOf(forLocaleTag("en")))
+        assertNull(tolgee.testResolveLocale(null))
+    }
+
+    @Test
+    fun returnsInputLocaleWhenNoAvailableLocales() {
+        val config = Tolgee.Config.Builder().build()
+        val tolgee = TestableTolgee(config)
+        val locale = forLocaleTag("zh-Hans")
+        val result = tolgee.testResolveLocale(locale)
+        assertEquals("zh-Hans", result?.toTag("-"))
+    }
+}