As the ちゅう in the 中s is rendakud you (I think?) would expect it to follow a similar pattern to words such as 近々「ちかぢか」as well as 鼻血「はなぢ」or even 気づく where the rendakud version of ち and つ stay. Is 年中 the weird one here? 近々? Is wanikani just weird for putting one standard for 近々 and they put it differently for 年中? Whats with the difference in standard 読み仮名?
Thanks for any help!
I didn’t went in deep search, but it seems to me that ぢ and づ are only used in kunyomi words, not onyomi (yes, that decision is quite arbitrary)
It may be that an onyomi word is less likely to be written in kana.
Or that onyomi pronunciations went over a much bigger sound change and orthographic reform (all those くわ>か、ちゃう>ちょう、かう>こう…)
Also 中-as-じゅう is not technically an example of rendaku, but rather just another reading that 中 can sometimes have.
I also see that ［音］チュウ（呉）（漢）ジュウ, but the same dictionary entry lists じゅう under チュウ.
In Wiktionary under Etymology 2, it simply says “The rendaku (連濁) form of chū above.”, without any citation, though on the Japanese counterpart, no particular claim is made.
At least, Japanese people here thinks it’s 和語系, so maybe really Rendaku’d?
The official government documentation of the new kana spelling talks about this case, in section 5 on that page. It starts off by stating the basic rule that you use 「ぢ」「づ」 for duplicated sounds (e.g. つづく（続)) and where compounding two words together has caused rendaku (e.g. はなぢ（鼻血)), and then it says there are some exceptions:
なお,次のような語については,現代語の意識では一般に二語に分解しにくいもの等として,それぞれ｢じ｣｢ず｣を用いて書くことを本則とし,「せかいぢゅう」「いなづま」のように「ぢ」「づ」を用いて書くこともできるものとする。
So the answer apparently is that for words like 年中, 世界中 and 稲妻 native speakers see them more as single indivisible words than as compounds with rendaku, even if that’s how they might have been originally formed. So the standard is to use じ and ず, though the use of ぢ and づ in these cases is not outright forbidden.
Other examples listed in this category are:
せかいじゅう（世界中）
いなずま（稲妻） かたず（固唾） きずな（絆＊） さかずき（杯） ときわず ほおずき みみずく
うなずく おとずれる（訪） かしずく つまずく ぬかずく ひざまずく
あせみずく くんずほぐれつ さしずめ でずっぱり なかんずく
うでずく くろずくめ ひとりずつ
ゆうずう（融通）
The document also says that for cases where the on-yomi has a voiced sound in it from the start, e.g. じめん（地面） ぬのじ（布地） ずが（図画） りゃくず（略図） , you use じ and ず because this isn’t voicing due to rendaku. But it does not put 世界中 in this category, so at least the authors of the kana spelling reform didn’t think of that as being “the on yomi of 中 here is じゅう”.
Thanks for the in depth reply! This makes a lot of sense