Here's how you translate them:
1. Download the language pack from Settings > Configure Chargebee > Customer-facing essentials > Languages.
2. In the pack, open your specific language's folder and you will find a file named "enums.csv" in the folder named 'internal'.
3. The enums.csv file will have different invoice keys where you can add the translated text to the value column of the key.
4. Finally, save the file in CSV format, zip the pack completely and then upload it to your site.