Google Translate is one of the available MT engines in Yaraku Translate, so I am worried about the security.

No secondary use of date is allowed when using Google Translate in Yaraku Translate. The same applies to the other engines.

We signed an NDA with the engines providers  to prevent secondary use of data of all the engines used in  Yaraku Translate.

Google Translate: See the highlighted parts in the following link "Google NDA" (Japanese only).

Microsoft Translate: https://www.microsoft.com/ja-jp/translator/business/notrace/

DeepL Translate: https://www.deepl.com/en/privacy

NICT Translate  (Everyone's Automatic Translation): https://www.k-intl.co.jp/minna_mt_kiyaku