my translation: [In Japanese, company name is written] Not formally as いすず but as いすゞ. In Chinese-language circle, [it is] 五十鈴 or 五十铃.
It is implied that in Japan, it is not (or no longer) 五十鈴 in traditional Chinese. But see (d)(ii): the river name, the eponym, remains 五十鈴川; in kanji, that is.
(b)
(i) In Japanese, There is a term 踊り字 (where 踊り odori means dancing -- because a word is repeated 繰り返し).
(ii) 踊り字 https://ja.wikipedia.org/wiki/踊り字
supplies the rule: use 々 to repeat a kanji; use ゝ (or ゞ of the original has two dots in the upper right corner) to repeat hiragana; and use ヽ (or ヾ) to repeat katakana.
(b) Jim Breen's Japanese-English dictionary:
* odoriji 踊り字; 踊字 【おどりじ】 (n): "iteration mark (used to represent repetition of the previous character)"
* 鈴 【すず[P[rincipal]; りん; れい[ok]】 (n): "bell (often globular)" (The りん (pronounced rin) or れい (pronounced rei, where ei signals a long vowel of e) are Chinese pronunciations of kanji 鈴.
* motsu 持つ 【もつ】 (v): "to hold (in one's hand)"
* miko 巫女[P]; 神子; 巫子 【みこ】 (n): "{Shinto} miko; shrine maiden; young girl or woman (trad. an unmarried virgin) who assists priests at shrines"
(c) Although 鈴 is often translated as bell and Isuzu, "fifty bells," it is really globular, but need not be enclosed on ALL sides. See photos in 鈴 https://ja.wikipedia.org/wiki/鈴
, where photo 2 (caption: 神楽鈴をもつ巫女) the woman folds in her right hand a bunch of 鈴; photo 3 four black bottom-less 鈴; photo 5 two big yellow 鈴 near the ceiling; and bottom photo, a horse decorated with two collars around neck and a belt around rump, all three with 鈴.
(d)
(i) Isuzu Motors does not have a page about its history or name origin. However, a source affiliated with the carmakers say:
Going forward together. Isuzu Trucks, undated https://www.isuzutruck.co.uk/about/history/
("Isuzu's origins can be traced right back to 1916, when the Tokyo Ishikawajima Shipbuilding & Engineering Company diversified into car production. In 1933 it launched a new car model and named it after a Japanese river. In fact, so popular was the car, the company decided to adopt the river’s name as its own company name – 'Isuzu.' Now, nearly a century later, Isuzu is proud to boast that its production lines are still flowing steadily – just like the river itself. Currently Isuzu’s main Fujisawa plant is operating a two, 8-hour shift pattern. You might be interested to know that during those shifts one Isuzu truck is produced every 1.5 minutes")
(ii)
(A) 五十鈴川 https://ja.wikipedia.org/wiki/%E ... 1%E9%88%B4%E5%B7%9D
is a 24-km long river in 三重県伊勢市 that runs by 伊勢神宮 (the oldest Shinto shrine in Japan; Shinto 神道 shrine is opposite of Buddhist temple)
(B) "translated into English its name means 'fifty bells' - the sound of the water flowing in the Isuzu River." from the Web.