[MangaDex] Language filter support

src/main/kotlin/org/koitharu/kotatsu/parsers/site/all/MangaDexParser.kt

@@ -79,6 +79,10 @@ internal class MangaDexParser(context: MangaLoaderContext) : MangaParser(context
 							MangaState.PAUSED -> append("hiatus")
 						}
 					}
+					filter.locale?.let {
+						append("&originalLanguage[]=")
+						append(it.language)
+					}
 				}
 
 				null -> {
@@ -183,6 +187,15 @@ internal class MangaDexParser(context: MangaLoaderContext) : MangaParser(context
 		}
 	}
 
+	override suspend fun getAvailableLocales(): Set<Locale> {
+		val head = webClient.httpGet("https://$domain/").parseHtml().head()
+		return head.getElementsByAttributeValue("property", "og:locale:alternate")
+			.mapNotNullToSet { meta ->
+				val raw = meta.attrOrNull("content") ?: return@mapNotNullToSet null
+				Locale(raw.substringBefore('_'), raw.substringAfter('_', ""))
+			}
+	}
+
 	private fun JSONObject.firstStringValue() = values().next() as String
 
 	private fun JSONObject.selectByLocale(): String? {

src/test/kotlin/org/koitharu/kotatsu/parsers/MangaParserTest.kt

@@ -115,6 +115,26 @@ internal class MangaParserTest {
 		assert(list.all { it.source == source })
 	}
 
+	@ParameterizedTest(name = "{index}|locale|{0}")
+	@MangaSources
+	fun locale(source: MangaSource) = runTest {
+		val parser = context.newParserInstance(source)
+		val locales = parser.getAvailableLocales()
+		if (locales.isEmpty()) {
+			return@runTest
+		}
+		val filter = MangaListFilter.Advanced(
+			sortOrder = parser.availableSortOrders.first(),
+			tags = setOf(),
+			locale = locales.random(),
+			states = setOf(),
+		)
+		val list = parser.getList(offset = 0, filter)
+		checkMangaList(list, filter.locale.toString())
+		assert(list.all { it.source == source })
+	}
+
+
 	@ParameterizedTest(name = "{index}|details|{0}")
 	@MangaSources
 	fun details(source: MangaSource) = runTest {