DeepL translate requests changed from get to post

[cboutaud]

Hi, it seems like DeepL translate requests changed from get to post back in march of this year, leading to "ServerException('ERR_BAD_REQUEST')" when using the DeeplTranslator translator

See: https://developers.deepl.com/docs/resources/breaking-changes-change-notices/march-2025-deprecating-get-requests-to-translate-and-authenticating-with-auth_key