feat(network): send Accept-Language header to addons

Adds an `Accept-Language` header on every addon HTTP call so Stremio-
compatible addons that maintain localized payloads (catalog names,
descriptions, …) can serve them in the user's language.

Resolution rules (mirrors NuvioTV PR #1766 with stricter region handling):

- User-picked in-app language (always region-less, e.g. `fr`):
  legacy behaviour `fr, en;q=0.7` — accept any French variant the addon serves.
- Otherwise device locale tag from `Locale.getDefault().toLanguageTag()` /
  `NSLocale.preferredLanguages.first`.
  - Regional locale (`fr-FR`, `pt-BR`, `es-MX`):
    strict chain `fr-FR, fr;q=0.9, en;q=0.5` — exact region first, then any
    variant of the same language, then English. Cross-region variants
    (e.g. `fr-CA`) are not preferred.
  - English (with or without region): tag itself, no q-suffix.
- Final fallback: `en`.

Header is added as a default — if the caller already specified
`Accept-Language` (case-insensitive), it is preserved untouched.

Affects every place in the app that displays a catalog name pulled from
an addon manifest: home rows, "see all" header, search → discover catalog
selector, addon reorder home catalogs screen, collection editor catalog
picker.

Adding a request header is fully backward-compatible — addons that
ignore it return identical payloads.

composeApp/src/androidMain/kotlin/com/nuvio/app/features/addons/AcceptLanguage.android.kt

@@ -0,0 +1,6 @@
+package com.nuvio.app.features.addons
+
+import java.util.Locale
+
+internal actual fun deviceLanguageTag(): String? =
+    Locale.getDefault().toLanguageTag().takeIf { it.isNotBlank() }

composeApp/src/androidMain/kotlin/com/nuvio/app/features/addons/AddonPlatform.android.kt

@@ -71,6 +71,13 @@ private fun Map<String, String>.withoutAcceptEncoding(): Map<String, String> =
 private fun Map<String, String>.getHeaderIgnoreCase(name: String): String? =
     entries.firstOrNull { (key, _) -> key.equals(name, ignoreCase = true) }?.value
 
+private fun Map<String, String>.withDefaultAcceptLanguage(): Map<String, String> =
+    if (getHeaderIgnoreCase("Accept-Language") != null) {
+        this
+    } else {
+        this + ("Accept-Language" to buildAcceptLanguageHeader())
+    }
+
 private data class LimitedReadResult(
     val bytes: ByteArray,
     val truncated: Boolean,
@@ -134,7 +141,7 @@ private suspend fun executeTextRequest(
     body: String = "",
 ): String = withContext(Dispatchers.IO) {
     val normalizedMethod = method.uppercase()
-    val sanitizedHeaders = headers.withoutAcceptEncoding()
+    val sanitizedHeaders = headers.withoutAcceptEncoding().withDefaultAcceptLanguage()
     val builder = Request.Builder().url(url)
     sanitizedHeaders.forEach { (key, value) ->
         builder.header(key, value)
@@ -214,7 +221,7 @@ actual suspend fun httpRequestRaw(
 ): RawHttpResponse =
     withContext(Dispatchers.IO) {
         val normalizedMethod = method.uppercase()
-        val sanitizedHeaders = headers.withoutAcceptEncoding()
+        val sanitizedHeaders = headers.withoutAcceptEncoding().withDefaultAcceptLanguage()
         val builder = Request.Builder().url(url)
         sanitizedHeaders.forEach { (key, value) ->
             builder.header(key, value)

composeApp/src/commonMain/kotlin/com/nuvio/app/features/addons/AcceptLanguage.kt

@@ -0,0 +1,50 @@
+package com.nuvio.app.features.addons
+
+import com.nuvio.app.features.settings.ThemeSettingsStorage
+
+/**
+ * Returns the device's primary BCP-47 language tag (e.g. "fr-FR", "en", "es-MX"),
+ * or `null` if the platform can't determine one.
+ */
+internal expect fun deviceLanguageTag(): String?
+
+/**
+ * Builds the value of the HTTP `Accept-Language` header that the addon HTTP
+ * client should send.
+ *
+ * Resolution rules:
+ * - If the user has explicitly picked an in-app language, that code wins
+ *   (the in-app language is always region-less, e.g. `fr`).
+ * - Otherwise the device locale tag is used.
+ *
+ * Header format:
+ * - Regional locale (`fr-FR`, `pt-BR`, `es-MX`): strict chain
+ *   `fr-FR, fr;q=0.9, en;q=0.5` — accept the exact region first, then any
+ *   variant of the same language, then English. Cross-region variants
+ *   (e.g. `fr-CA`) are not preferred.
+ * - Language only (`fr`): legacy behaviour `fr, en;q=0.7` — any French variant
+ *   the addon serves is acceptable.
+ * - English (with or without region): just the tag itself, no q-suffix.
+ */
+internal fun buildAcceptLanguageHeader(): String {
+    val rawTag = ThemeSettingsStorage.loadSelectedAppLanguage()?.takeIf { it.isNotBlank() }
+        ?: deviceLanguageTag()?.takeIf {
+            it.isNotBlank() && !it.equals("und", ignoreCase = true)
+        }
+        ?: return "en"
+
+    val normalized = rawTag.replace('_', '-').trim()
+    val parts = normalized.split('-', limit = 2)
+    val language = parts[0].lowercase().takeIf { it.isNotBlank() } ?: return "en"
+    val region = parts.getOrNull(1)?.takeIf { it.isNotBlank() }?.uppercase()
+
+    if (language == "en") {
+        return if (region != null) "en-$region, en" else "en"
+    }
+
+    return if (region != null) {
+        "$language-$region, $language;q=0.9, en;q=0.5"
+    } else {
+        "$language, en;q=0.7"
+    }
+}

composeApp/src/iosMain/kotlin/com/nuvio/app/features/addons/AcceptLanguage.ios.kt

@@ -0,0 +1,9 @@
+package com.nuvio.app.features.addons
+
+import platform.Foundation.NSLocale
+import platform.Foundation.preferredLanguages
+
+internal actual fun deviceLanguageTag(): String? {
+    val preferred = NSLocale.preferredLanguages.firstOrNull() as? String
+    return preferred?.takeIf { it.isNotBlank() }
+}

composeApp/src/iosMain/kotlin/com/nuvio/app/features/addons/AddonPlatform.ios.kt

@@ -46,10 +46,21 @@ private val addonHttpClient = HttpClient(Darwin) {
     expectSuccess = false
 }
 
+private fun Map<String, String>.hasHeaderIgnoreCase(name: String): Boolean =
+    keys.any { it.equals(name, ignoreCase = true) }
+
+private fun Map<String, String>.withDefaultAcceptLanguage(): Map<String, String> =
+    if (hasHeaderIgnoreCase("Accept-Language")) {
+        this
+    } else {
+        this + ("Accept-Language" to buildAcceptLanguageHeader())
+    }
+
 actual suspend fun httpGetText(url: String): String =
     addonHttpClient
         .get(url) {
             accept(ContentType.Application.Json)
+            header(HttpHeaders.AcceptLanguage, buildAcceptLanguageHeader())
         }
         .let { response ->
             val payload = response.bodyAsText()
@@ -67,6 +78,7 @@ actual suspend fun httpPostJson(url: String, body: String): String =
         .post(url) {
             accept(ContentType.Application.Json)
             header(HttpHeaders.ContentType, ContentType.Application.Json.toString())
+            header(HttpHeaders.AcceptLanguage, buildAcceptLanguageHeader())
             setBody(body)
         }
         .let { response ->
@@ -87,7 +99,7 @@ actual suspend fun httpGetTextWithHeaders(
     addonHttpClient
         .get(url) {
             accept(ContentType.Application.Json)
-            headers.forEach { (key, value) ->
+            headers.withDefaultAcceptLanguage().forEach { (key, value) ->
                 header(key, value)
             }
         }
@@ -111,7 +123,7 @@ actual suspend fun httpPostJsonWithHeaders(
         .post(url) {
             accept(ContentType.Application.Json)
             header(HttpHeaders.ContentType, ContentType.Application.Json.toString())
-            headers.forEach { (key, value) ->
+            headers.withDefaultAcceptLanguage().forEach { (key, value) ->
                 header(key, value)
             }
             setBody(body)
@@ -138,7 +150,7 @@ actual suspend fun httpRequestRaw(
         .request {
             url(url)
             this.method = HttpMethod.parse(method.uppercase())
-            headers.forEach { (key, value) ->
+            headers.withDefaultAcceptLanguage().forEach { (key, value) ->
                 header(key, value)
             }
             if (this.method == HttpMethod.Post || this.method == HttpMethod.Put || this.method == HttpMethod.Patch) {