target_lang、source_langともに言語指定は以下のようになる（deepl公式サイトより）。
"BG" - Bulgarian
"CS" - Czech
"DA" - Danish
"DE" - German
"EL" - Greek
"EN-GB" - English (British)
"EN-US" - English (American)
"EN" - English (unspecified variant for backward compatibility; please select EN-GB or EN-US instead)
"ES" - Spanish
"ET" - Estonian
"FI" - Finnish
"FR" - French
"HU" - Hungarian
"IT" - Italian
"JA" - Japanese
"LT" - Lithuanian
"LV" - Latvian
"NL" - Dutch
"PL" - Polish
"PT-PT" - Portuguese (all Portuguese varieties excluding Brazilian Portuguese)
"PT-BR" - Portuguese (Brazilian)
"PT" - Portuguese (unspecified variant for backward compatibility; please select PT-PT or PT-BR instead)
"RO" - Romanian
"RU" - Russian
"SK" - Slovak
"SL" - Slovenian
"SV" - Swedish
"ZH" - Chinese
技術資料
www.deepl.com
