Go to https://www.deepl.com, paste this code into your browser console, and execute "translateAll" with a key-value object as the first param.

translate.js

function waitUntilValueChanges(domElem) {
  return new Promise(resolve => {
    let prevVal = domElem.value;
    const inter = setInterval(() => {
      if (domElem.value !== prevVal) {
        clearInterval(inter);
        return resolve();
      }
      prevVal = domElem.value + '';
    }, 100);
  })
}

async function translateAll(obj) {
  let newObj = {};
  for (const currKey in obj) {
    const oldVal = obj[currKey];
    if (oldVal) continue;
    $('.lmt__textarea.lmt__source_textarea.lmt__textarea_base_style')[0].value = currKey;
    $('.lmt__textarea.lmt__source_textarea.lmt__textarea_base_style')[0].dispatchEvent(new Event('change', { value: 't' }));
    await waitUntilValueChanges($('.lmt__textarea.lmt__target_textarea.lmt__textarea_base_style')[0]);
    const translated = $('.lmt__textarea.lmt__target_textarea.lmt__textarea_base_style')[0].value;
    newObj = {
      ...newObj,
      [currKey]: translated
    }
  }
  console.log(newObj);
  return newObj;
}