Below is my reply to the above comment on Rangyayo Yenmun (Korean Hangul) sent by a Korean conlanger.
I hope it doesn't give him/her the idea that I'm being defensive lol...
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Seeing that Rangyayo is using a mixed script of Hanji and Yenmun (Hanja and Hangul), how cool is that to have a native Korean conlanger commented on my conlang.
I was excited and thrilled!
For the phonetic values, you are right that some of them represented by Rangyayo Yenmun are different from that represented by nowadays Korean Hangul. However, somehow there are traces for us to believe that the Rangyayo version of phonetic values may be closer to what the Hangul alphabet were originally pronounced in the document of Hunminjeongeum (corresponding to the Middle Korean language).
First of all, Hunminjeongeum states that the doubled letters were once used to represent voiced consonants 전 탁음 자(全濁音字) - ㄲ /g/, ㄸ /d/, ㅃ /b/... ㅉ, ㅆ, ㆅ. And for vowel letter ㅓ, if we compare the corresponding Sino pronunciations of the Hanja that contains the vowel ㅓ, we are able to conclude that ㅓ is actually closer to /e/ in Middle Korean rather than /ɤ/ in Modern Korean (there could be a vowel shift when Middle Korean has evolved into Modern Korean). For example 선(鮮)is /ɕiɛn/ in Chinese, /sen/ in Japanese and /tiên/ in Vietnamese; and 건(健)is /tɕiɛn/ in Chinese, /ken/ in Japanese and /kiện/ in Vietnamese. And diphthong letters ㅐ ㅔ ㅚ may originally represent diphthongs in Middle Korean but have undergone monophthongization and become monophthongs in Modern Korean. For example, 새(賽)is /sai/ in Chinese, /sai/ in Japanese and /tái/ in Vietnamese.
About the pronunciations of Rangyayo Hanji, nearly each Hanji has two pronunciations, like 食, the first one is the native pronounciation /ya/ as in 食쁘 /yabu/ "eat", the second one is the Sino pronouncation /jik/ as in 食塩 /jikyem/ "table salt (salt for eating)". The relationships between the two pronunciations can be paralleled with Kunyomi and Onyomi in Japanese
--Deslee (talk) 12:28, November 12, 2013 (UTC)
The main reason why you were not very impressed with the phonetic values of Rangyayo Yenmun, can be that the Hangul alphabet is only used by one language, the Modern Korean language. If it were used by more than one language like the Latin alphabet, in which many letters represent different phonemes in different languages, the Rangyayo version would be easier to swallow than it is now. For example, the Latin letter Y, has the sound values /j/ /i/ /ai/ in English but /y/ or /ʏ/ in the Scandinavian languages and in German; J has the sound values /dʒ/ in English but it is the palatal approximant /j/ in the great majority of other Germanic languages, Uralic and Slavic languages that use the Latin alphabet, and it is /x ~ h/ in Spanish and /ʒ/ in many other Romance languages.--Deslee (talk) 13:16, November 12, 2013 (UTC)