For your questions "can this be done in Excel", I believe the short answer is no. There is not a native translation service there, as you have noted. Moving that much data in/out piecemeal is obviously not reasonable.

Excel Power Query won't let you call a DLL or external code unless you write your own connector.

If you're going to be doing this often, then maybe it is worth considering writing a connector for Power Query (https://learn.microsoft.com/en-us/power-query/install-sdk) or an Excel Add-In that completes this step.

PowerBI is for visualisation and reporting. It does include some translation tools. If you're just interested in translating a large volume of structured data, however, BI is probably not the right tool.

Especially if this is a one-off task, I suggest you check the built-in GOOGLETRANSLATE() function in Google Sheets: https://support.google.com/docs/answer/3093331?hl=en . If you actually need to produce an Excel file or BI presentation afterward, you can export the translated data back to Excel and proceed.