I must agree that sometimes it is pure laziness. But people have been doing that for ages. It was probably a lazy English person who decided that the French word "porc" would be nice to have in English to refer to pig meat. ;-).
But sometimes the foreign word has a special meaning which makes it hard to translate. Referring to your example in Chinese: I guess most people would not translate the words 'yin' and 'yang'. And in Duolingo the word gladiator is also not translated.
So you could argue that it is difficult to translate 'paterfamilias' into English because the concept does not exist anymore in modern society.
I agree with your sentiment overall, Jef, but I wouldn't call those English who started referring to pig meat as pork "lazy"! On the contrary they were the hard-working peasants who herded swine on the land and the serving people who cooked it for their new Norman masters who had to say "Here is your 'porc', sire". The same goes for ox / bœuf (beef), calf / veau (veal), and sheep / mouton (mutton).
I think it's not possible to capture all the meanings of paterfamilias in a sentence, or you would say "patriarch-who-has-all-the-right-upon-his-family-and-extended-family", or something like this. As you wouldn't capture all the meanings for "samourai" in a sentence, because, like paterfamilias, it is a very cultural-specific thing.
But I guess "patriarch" is a good translation too, (if we really need to translate the word) as it captures the meaning of elder male in the family, always including much respect from the other members, (and usually including a kind of power).