I often thought of asking my father why he studied the German language in the "20's" to the point of becoming completely fluent and literate in all aspects and a noted scholar at the time.
During the 30's, when Germany was rising from the ashes of WW1, a new populism and confidence had started to develop. This then led to more students seeking to improve their ability to communicate and trade with what was being seen as an emerging power. So I put it down to a simple desire to improve his job prospects.
It made sense to me, but oddly, even before the start of WW2, he no longer pursued any interest in the language and would only bring it out of the closet as a party trick much later to surprise people. Was he involved in something which he never spoke of? Unfortunately I did not have the opportunity to have a conversation about it which I now much regret.
It will be worthwhile not to let this small piece of history in your family slip by.
IG