Renars here from Excelify.
Sorry about replying in English here.
You sure can bulk update Product details, including inventory with Excelify!
Having characters in other languages should not cause any issues with Excel files and Excelify exports and imports.
Here we do have a great tutorial that explains more on how to use Excelify to bulk update inventory levels.
If you do not wish for an app to transliterate Product Handles to the English alphabet when importing, you can un-select the import option "Transliterate Handles to English alphabet".
If this is something that you could be interested in then please reach out to Excelify Japanese support directly.