I'm reminded of my former neighbors, who would switch between English and Spanish mid-sentence. I asked them about it once and they expressed a sentiment similar to yours.
As an English and German speaker, my kids would tell you I sometimes do the same thing. Bad drivers get yelled at in German ;-D
But on the other hand that makes german much longer. Translations into german (e.g. SW or movie subtitles) are the longest in german than in any other major language. You need much more room to express the same. E.g. in SW translations this conciseness strikes back, the english original form is often preferred, as it is easier to understand and not as baroque as the german form.
In Japanese forced with the same problem of having to import many new foreign terms ("lehnworte"), they chose a better way, Katakana, which is almost as well modernized as Korean. In German it backfired, and instead of chosing modern shorter and more precise forms, they want for the longer nouns, adding to it.
I can believe that if you translate texts that are written in idiomatic English into German, they get longer. On the other hand, if you have a concisely written scientific text in German, translating it into English leads to something between gibberish and something barely readable. So you often have to completely rewrite/reexpress large parts of the text so that it looks like idiomatic English.
As a native German speaker, I disagree. German allows a really concise nominal style that is hard to express in English.