Why Korean transcriptions of Japanese words uses the letters ㄱ,ㄷ,ㅈ for initial /k/, /t/, /tɕ/ while using ㅋ,ㅌ,ㅊ for other languages?

Question

Looking at Korean transcription rules for Japanese, I noticed that for some consonants, the hangul transcription would change if it was in the initial position:

https://kornorms.korean.go.kr//regltn/regltnView.do?regltn_code=0003#a

カ /ka/ is transcribed 가 in the inital position, but 카 in medial of final positions. So the word カタカナ is transcribed 가타카나. ガ /ga/ is always transcribed as 가.

The same thing happens with /t/ and /tɕ/, so: タ /ta/ is 다 initally, but 타 medially and finally. So たれ (tare, "sauce") and だれ (dare, "who") are both transcribed 다레. The same happens with チ, 지 initially and 치 in other positions. The Korean Wikipedia article for ちょんまげ "chonmage", features both 촌마게 and 존마게 as a transcription.

Curiously, it does not happen with /p/, that is always transcribed as ㅍ.

This does not happen in the transcription rules for other languages, where seens to be /k/,/t/, tɕ/tʃ are consistently written as ㅋ,ㅌ,ㅊ even in the inital position:

English: cat 캣, time 타임, chart 차트.

Spanish: colcren 콜크렌, chicharra 치차라, tetraetro 테트라에트로.

Italian: Como 코모, Torino 토리노.

Portuguese: Cabral 카브랄, Coelho 코엘류, Tavira 타비라

So why Korean transcriptions of Japanese words uses the letters ㄱ,ㄷ,ㅈ for initial /k/, /t/, /tɕ/ while using ㅋ,ㅌ,ㅊ for other languages? What are the phonological or historical reasons for this different treatment when transcribing Japanese to Hangul specifically?

Other links:

http://kkeutsori.com/loanword-transcription-rules/japanese/

http://kkeutsori.com/loanword-transcription-rules/portuguese/

http://kkeutsori.com/loanword-transcription-rules/english-german-and-french/

Edit: I think @jogloran explained well why ㄱ,ㄷ,ㅈ are used for the Japanese initial unvoiced stops and the article explains these and other transcription conventions in depth. The use of ㅋ,ㅌ,ㅊ for English initial unvoiced stops, that are more aspirated than the Japanese ones, is clear to me now too. But the question remains as why other languages that have initial stops with even less aspiration than their Japanese counterparts, such as Portuguese, use ㅋ,ㅌ,ㅊ in their official hangulizations.

Answer 1

As you may know, "single" stops in Korean are weakly aspirated in initial position only (audio example), so Japanese stops in the unvoiced series (such as た) correspond to Korean "single" stops (e.g. ㄷ) in initial position. They are not perceived as ㅌ because the aspirated series in initial position in Korean is much more strongly aspirated than in Japanese.

Section 5 of Ito et al. was an attempt to explain the second part of your question -- why loanwords from other languages do utilise the aspirated series to correspond to aspirated/non-aspirated distinctions in those languages. The paper mentions French and English as languages where the mapping of aspirated stops seems to differ to that of Japanese. The key observation on p. 93 was:

Japanese voiceless stops have a VOT that is too brief to be identified with a Korean aspirated stop

They argued that even though this left Korean unable to distinguish the aspirated from the unaspirated series in initial position in Japanese loanwords, the perceptual match was large enough for Koreans that they would both map onto the Korean "single" stop series.

References

Ito et al. (2006): The adaptation of Japanese loanwords into Korean. Studies in Loanword Phonology (MITWPL 52).

Answer 2

jogloran's answer is a good explanation on why it's possible to transcribe word-initial /k/, /t/ to Korean ㄱ and ㄷ. As for why it had to be that way, there's no logical answer - IMHO the other way (always transcribing /k/ to ㅋ, for example) makes just as much sense, but when the rule was decided, apparently the scholars liked the current scheme better.

If we had consulted a different group of scholars, the decision could have gone the other way, but once these decisions were made, millions of books would start to use the official scheme - just by being official, it becomes harder and harder to change.

That also partly explains your question about "Why not Spanish or Italian?" Obviously, the transcription rules for Spanish were made by experts on Spanish (or at least I hope so) - they were a totally different group of people, and there would be no reason to expect them to talk to Japanese experts to keep things consistent.

In fact, the official Japanese transcription rule is still controversial and not universally accepted. You can easily see it in the Korean fandom of Japanese popular culture (games or anime), where people frequently use ad-hoc schemes that are more faithful to the original Japanese sound system. For example, here's a Korean wiki site listing Japanese animation directors: you can see many names starting with ㅋ or ㅌ, which would be written with ㄱ/ㄷ under the official scheme.

Answer 3

For what it's worth, I think all comments made here to the effect that the Korean spelling of カタカナ as 가타카나 is due to VOT in either language are not correct or at least insufficient for modern speakers of Korean (it might have been different in the past). The indication for this is that not only does the Korean Wikipedia page for Tokyo say

도쿄도(일본어: 東京都 발음: '토쿄토')

(i.e. effectively "Tokyo is written in Korean as 도쿄도 and pronounced as '토쿄토'), but also the page about Katakana has consistently transcribed カ as 카 and ガ as 가. So writing 가 for カ is a historical artifact rather than what people would reach for if they had to devise a transcription today.

By the way the surprising Korean spelling may be compared to what is done in German; when you visit the German page about Tokyo you will find "Tokio (auch Tokyo, japanisch 東京 Tōkyō [to̞ːkjo̞ː])" next to spellings like "Tokugawa Ieyasu" and "Kyōto". The last one would be highly unusual for newspapers (Wikipedia opines "Kyōto, im Deutschen meist Kyoto, seltener auch Kioto geschrieben", but in my experience both Kioto and Kyoto can be frequently found). The fact is that a lot of times, German articles about Japan will use a different spelling for the new and the old capital but prefer the international / English spellings for all lesser place names (the same being true for Pyongyang, which is rendered as Pjöngjang, retaining an older spelling, which is add odds with the usage for all other Korean place names).