google_translate_api.js

// modify https://qiita.com/satto_sann/items/be4177360a0bc3691fdf

function doPost(e) {
    const params = JSON.parse(e.postData.getDataAsString());
    const translated_text = LanguageApp.translate(params.text, params.source, params.target);

    let body;
    if (translated_text) {
        body = {
          code: 200,
          text: translated_text
        };
    } else {
        body = {
          code: 400,
          text: "Bad Request"
        };
    }

    let response = ContentService.createTextOutput();
    response.setMimeType(ContentService.MimeType.JSON);
    response.setContent(JSON.stringify(body));

    return response;
}