For test, I translated a document from English to Spanish, it did changes all the fonts to Calibri.
The translate tool’s font may be subject to the default font and size in the Normal.dotm file.
So I’m afraid that it cannot retain the fonts in the original document.
As a workaround to retain the font of the original document, please make sure that the preferred font (the most frequently used font in the original document) is set as default. Then you could change the font of different part.
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