fix: pass language to Collabora file conversions

lib/Conversion/ConversionProvider.php

@@ -165,7 +165,18 @@ public function convertFile(File $file, string $targetMimeType): mixed {
 			}
 		}
 
-		return $this->remoteService->convertFileTo($file, $targetFileExtension);
+		return $this->remoteService->convertFileTo(
+			$file,
+			$targetFileExtension,
+			conversionOptions: ['lang' => $this->getConversionLanguage()]
+		);
+	}
+
+	private function getConversionLanguage(): string {
+		$locale = $this->l10n->getLocaleCode();
+		$language = $locale !== '' ? $locale : $this->l10n->getLanguageCode();
+
+		return str_replace('_', '-', $language);
 	}
 
 	private function getMimeProvidersFor(array $inputMimeTypes, string $outputMimeType): array {

lib/Service/RemoteService.php

@@ -58,21 +58,28 @@ public function fetchTargetThumbnail(File $file, string $target): ?string {
 	}
 
 	/**
+	 * @param array<string, string> $conversionOptions
 	 * @return resource|string
 	 */
-	public function convertFileTo(File $file, string $format, int $timeout = RemoteOptionsService::REMOTE_TIMEOUT_DEFAULT) {
+	public function convertFileTo(
+		File $file,
+		string $format,
+		int $timeout = RemoteOptionsService::REMOTE_TIMEOUT_DEFAULT,
+		array $conversionOptions = [],
+	) {
 		$fileName = $file->getStorage()->getLocalFile($file->getInternalPath());
 		$stream = fopen($fileName, 'rb');
 
 		if ($stream === false) {
 			throw new Exception('Failed to open stream');
 		}
 
-		return $this->convertTo($file->getName(), $stream, $format, [], $timeout);
+		return $this->convertTo($file->getName(), $stream, $format, $conversionOptions, $timeout);
 	}
 
 	/**
 	 * @param resource $stream
+	 * @param array<string, string>|null $conversionOptions
 	 * @return resource|string
 	 */
 	public function convertTo(string $filename, $stream, string $format, ?array $conversionOptions = [], int $timeout = RemoteOptionsService::REMOTE_TIMEOUT_DEFAULT) {
@@ -86,13 +93,20 @@ public function convertTo(string $filename, $stream, string $format, ?array $con
 		}
 
 		$options['multipart'] = [
-			array_merge([
+			[
 				'name' => $filename,
 				'filename' => $filename,
 				'contents' => $stream
-			], $conversionOptions),
+			],
 		];
 
+		foreach ($conversionOptions ?? [] as $name => $contents) {
+			$options['multipart'][] = [
+				'name' => (string)$name,
+				'contents' => $contents,
+			];
+		}
+
 		try {
 			$response = $client->post($this->appConfig->getCollaboraUrlInternal() . '/cool/convert-to/' . $format, $options);
 			$body = $response->getBody();

tests/lib/Conversion/ConversionProviderTest.php

@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace Tests\Richdocuments\Conversion;
+
+use OCA\Richdocuments\Conversion\ConversionProvider;
+use OCA\Richdocuments\Service\RemoteOptionsService;
+use OCA\Richdocuments\Service\RemoteService;
+use OCA\Richdocuments\Service\SecureViewService;
+use OCP\Files\File;
+use OCP\IL10N;
+use OCP\L10N\IFactory;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+
+class ConversionProviderTest extends TestCase {
+	private RemoteService&MockObject $remoteService;
+	private LoggerInterface&MockObject $logger;
+	private IFactory&MockObject $l10nFactory;
+	private IL10N&MockObject $l10n;
+	private SecureViewService&MockObject $secureViewService;
+	private ConversionProvider $provider;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->remoteService = $this->createMock(RemoteService::class);
+		$this->logger = $this->createMock(LoggerInterface::class);
+		$this->l10nFactory = $this->createMock(IFactory::class);
+		$this->l10n = $this->createMock(IL10N::class);
+		$this->secureViewService = $this->createMock(SecureViewService::class);
+
+		$this->l10n->method('t')->willReturnCallback(static fn (string $text): string => $text);
+		$this->l10nFactory->method('get')
+			->with('richdocuments')
+			->willReturn($this->l10n);
+
+		$this->provider = new ConversionProvider(
+			$this->remoteService,
+			$this->logger,
+			$this->l10nFactory,
+			$this->secureViewService,
+		);
+	}
+
+	public function testConvertFilePassesCurrentLocaleToCollabora(): void {
+		$file = $this->createMock(File::class);
+
+		$this->l10n->expects($this->once())
+			->method('getLocaleCode')
+			->willReturn('de_DE');
+		$this->secureViewService->method('isEnabled')
+			->willReturn(false);
+		$this->remoteService->expects($this->once())
+			->method('convertFileTo')
+			->with($file, 'pdf', RemoteOptionsService::REMOTE_TIMEOUT_DEFAULT, ['lang' => 'de-DE'])
+			->willReturn('pdf-content');
+
+		$result = $this->provider->convertFile($file, 'application/pdf');
+
+		$this->assertSame('pdf-content', $result);
+	}
+}

tests/lib/Service/RemoteServiceTest.php

@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace Tests\Richdocuments\Service;
+
+use OCA\Richdocuments\AppConfig;
+use OCA\Richdocuments\Service\CapabilitiesService;
+use OCA\Richdocuments\Service\RemoteService;
+use OCP\Http\Client\IClient;
+use OCP\Http\Client\IClientService;
+use OCP\Http\Client\IResponse;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+
+class RemoteServiceTest extends TestCase {
+	private AppConfig&MockObject $appConfig;
+	private IClientService&MockObject $clientService;
+	private IClient&MockObject $client;
+	private CapabilitiesService&MockObject $capabilitiesService;
+	private LoggerInterface&MockObject $logger;
+	private RemoteService $service;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->appConfig = $this->createMock(AppConfig::class);
+		$this->clientService = $this->createMock(IClientService::class);
+		$this->client = $this->createMock(IClient::class);
+		$this->capabilitiesService = $this->createMock(CapabilitiesService::class);
+		$this->logger = $this->createMock(LoggerInterface::class);
+
+		$this->clientService->method('newClient')
+			->willReturn($this->client);
+
+		$this->service = new RemoteService(
+			$this->appConfig,
+			$this->clientService,
+			$this->capabilitiesService,
+			$this->logger,
+		);
+	}
+
+	public function testConvertToSendsConversionOptionsAsMultipartFields(): void {
+		$stream = fopen('php://memory', 'r+');
+		$response = $this->createMock(IResponse::class);
+
+		$this->appConfig->method('getCollaboraUrlInternal')
+			->willReturn('http://cool.example');
+		$this->appConfig->method('getDisableCertificateValidation')
+			->willReturn(false);
+		$response->method('getBody')
+			->willReturn('converted-content');
+
+		$this->client->expects($this->once())
+			->method('post')
+			->with(
+				'http://cool.example/cool/convert-to/pdf',
+				$this->callback(function (array $options) use ($stream): bool {
+					$this->assertSame([
+						[
+							'name' => 'document.xlsx',
+							'filename' => 'document.xlsx',
+							'contents' => $stream,
+						],
+						[
+							'name' => 'lang',
+							'contents' => 'de-DE',
+						],
+					], $options['multipart']);
+
+					return true;
+				})
+			)
+			->willReturn($response);
+
+		$result = $this->service->convertTo('document.xlsx', $stream, 'pdf', ['lang' => 'de-DE']);
+
+		$this->assertSame('converted-content', $result);
+	}
+}