Vadim Berman Thanks for sharing the exact page. I think as per the current requirements your scenario does seem to fall under the restrictions if the user results are not used for display purposes. However, as you may have noticed that there is a non-display URL discovery terms that you can review and check if the search is made for discovery purpose if initiated by user. However, this also has restrictions on improve services that you or third parties might offer.
Is there a simple stripped down corpus-like search API, Bing or not?
For the above question, there is no stripped-down version of bing. Since you have mentioned using the words to lookup in foreign languages you might want to check out Azure translator service.