I can second that with two
languages wholeheartedly. And I was lucky to grow up speaking German and English simultaneously, as my parents and I spent the first 19 years of my life basically in English-speaking foreign countries. And I have one book by JRRT edited by Christopher, the 2007 "
The Children of Húrin", in German translation and English original (after having bought the German translation at a rather run-of-the-mill bookshop, I popped over to a more specialized one across the street to order the English original). Having read these two in a short period of time, practically back-to-back, I noticed the difficulty of translating "Silmarillion stuff" into German. We do have a German translation of LoTR that I have read, which I bought for my wife over 20, perhaps over 30 years ago. But I never read the English and German versions shortly after one another, so I don't have that kind of a comparison.
Now German and English have common roots (English being more closely related to the northern German dialects than to south German Bavarian or Swabian). Of course English was polluted by that Latin-derived stuff from Normandy
, but there are still many similarities. But the "Silmarillion" stuff with its almost consistently archaic language is definitely difficult to translate. Even for the less demanding LoTR, I have this general feeling that the many language subtleties that JRRT was capable of and employed (again something the obtuse among his critics failed to grasp) get "lost in translation". Words can have several meanings or, more difficult, allusions. And while the may be an overlap between the meanings of these word in both language, the crucial one might just happen to be one that does not occur in the other language - this would be German.