cat /dev/random meh

dl() {
  # Read text from stdin
  local text=$(cat -)
  # Set the API endpoint and your Deepl API key
  local endpoint="https://api-free.deepl.com/v2/translate"
  local api_key="$your_deepl_api_key"
  local target_lang="EN"
  # Set the target language to English
  local out=$(curl -s -X POST "$endpoint" -H "Content-Type: application/x-www-form-urlencoded" -d "auth_key=$api_key&text=$text&target_lang=$target_lang")

  local language=$(echo $out | jq -r '.translations[0].detected_source_language')
  # Set the target language based on the detected language
  if [ "$language" = "EN" ]; then
    local target_lang="ZH"
    local out=$(curl -s -X POST "$endpoint" -H "Content-Type: application/x-www-form-urlencoded" -d "auth_key=$api_key&text=$text&target_lang=$target_lang")
  fi
  # Extract the translated text from the API response using jq
  echo "$out" | jq -r '.translations[0].text'
}

Usage:
$ echo '你好世界' | dl
Hello World
$ echo 'Hello World' | dl
你好，世界