Prof Wälchli, the author of the book found by htatsuha, included ASL in his study. I had forgotten that there's another currently active way to "write" that's based on meaning rather than sound, not just Chinese. APPLE•BANANA•ORANGE (in this order) means "fruits". That's kind of a 3-kanji tautological :).
Here's a couple more thoughts: if I'm right about the fact that Chinese writing creates tautologicals, then there should be quite a lot in Vietnamese, despite this language not being agglutinative, with the creation of new tautologicals pretty much over a few decades after the introduction of the Latin alphabet by the French (around 1800, I think). And there should be somewhat fewer of them being created in Korean (agglutinative) since the creation of Hangul. Mayan languages also are agglutinative, and until Western Civilization ravaged Mexico and Central America as some kind of Genghis Khan on steroids (populations divided by ~25 during the "golden century" of Spain), they had a very complex writing system (too obscure to have influenced the language?). So that's one more language a linguist could look at to study this phenomenon.
So, it took a Japanese scholar barely one minute to find the one French tautological : aujourd'hui. hui (see Spanish hoy) is the contraction of hoc dies, so "aujourd'•hui" is built as "at the day of •this day". Congratulations, カズさん! And this made me think that there could be at least a few German tautologicals. Compounding is not quite the same as agglunating, and I'm still confident that agglutination (膠着 -> 膠着語) creates tautologicals, but is it really that agglutinating Georgian, Mordvin etc (Hungarian?) have quite a few, and compounding German has zero? The documents mentioned above claimed there are no such words in Standard European languages, but if they had asked カズさん, they would have known about aujourd'hui. Anyway, more than 200, now, in the 2 lists combined, I'm rather confident no other language has so many (and obviously those lists are still very far from complete).
Also, I just realized... My Greek is still very basic, but I know a postman is a fast•road, a bus is a people•carrier, a giraffe is a camel•leopard (the word camelopardalis / cameleopard still survives in astronomy and biology). Compounding in the Classical era was so out of control that Aristophanes, in a play against democracy (what's next? Women in politics?, those Athenian hipsters be tripping! Cf. "Assemblywomen") made fun of it by inventing the λοπαδοτεμαχοσελαχογαλεοκρανιολειψανοδριμυποτριμματοσιλφιοκαραβομελιτοκατακεχυμενοκιχλεπικοσσυφοφαττοπεριστεραλεκτρυονοπτοκεφαλλιοκιγκλοπελειολαγῳοσιραιοβαφητραγανοπτερύγων. It's the name of a dish that contains the recipe! If you can say it, you can prepare it, brilliant! So... Greek has plenty of compounds, and it's probably only a matter of time before I come up with at least a Greek tautological, despite what experts said... But even then, the difficulty to find any at all underlines the specificity of Japanese. Among the ~140 tautologicals in the list, there are many that I found by simply wondering "Hey, if I combine 2 kanjis meaning so-and-so, would I get a word meaning the same?... Yup!", and many more I found by reviewing common vocab (N3-ish).
Thanks Karlla, that's quite an interesting too, because although the tautological meaning still exists, the most common meaning is quite different, a bit like 左右. Besides this, I found that I was right about Korean, they also have quite a lot of them, but now many of them aren't obvious to see, because they stopped using Chinese characters. 舞踊, for example, is muyong, but now that it's written in Hangul, ithe origin is not obvious. And, probably, they don't make new words by agglutinating kanji anymore, so they don't make new ones like these... Actually, a Korean explained to me that infact new tautologicals keep popping up in Korean, ptecisely because most people don't know the Chinese characters' meanings and therefore how half off Korean words are formed. Here's a page that mentions quite a lot of examples. It's useable with an auto-translator. https://namu.wiki/w/%EA%B2%B9%...
I'm a bit uncertain about 責任. If you ask the kanji dictionary, you'll get different meanings for those kanji, but when you look up 責 in the vocab dictionary, you'll find that it means "responsibility, duty, obligation" which is pretty much the same as 任. What do you think?