Parallels in Allophonic Variation in Korean and Thai

I have recently started learning Thai. In several ways, it is unlike any language I've studied before: it is tonal, and lacks any grammatical inflection. However, the sound system strangely reminds me a lot of Korean. In particular, both languages have a similar use of allophones depending on whether a phoneme occurs at the beginning or end of a syllable. A lot of these similarities stem from the fact that both Korean and Thai have a strict syllable structure. I am not suggesting any formal relationship between the two languages, though: these are simply my observations.

Aspiration and voicing

Both Korean and Thai have contrastive aspiration on the sounds /p/, /t/, and /k/. In both languages, when a stop sound occurs at the end of a syllable, it is unreleased. Therefore, when the aspirated phonemes /pʰ/, /tʰ/, and /kʰ/ occur at the end of a syllable, they lose their aspirated quality in both languages.

• Korean ㅌ: initial 털 /tʰʌl/ "hair" vs. final 팥 /pʰat̚/ "red bean" 
• Thai ท: initial ทอง /tʰɔːŋ/ "gold" vs. final บาท /bà:t̚/ "baht"

A similar thing happens to voiced sounds, which become their voiceless equivalents at the end of a syllable. Note that in Korean, these sounds are only voiced when surrounded by other voiced sounds.

• K. ㅂ: medial 아버지 /abʌd͡ʑi/ "father" vs. final 입 /ip̚/ "mouth, lips"
  
• T. ด: initial ดี /di:/ "good" vs. final เจ็ด /t͡ɕèt̚/ "seven"

Alternation of s, j, and ch with t at the end of syllables

When the sounds /s/, /t͡ɕ/, and /t͡ɕʰ/ appear at the end of the syllable, in both Korean and Thai, all three become /t̚/.

• K. ㅅ: initial 산 /san/ "mountain" vs. final 맛 /mat̚/ "flavor"
• T. ศ: initial ศูนย์ /sǔːn/ "zero" vs. final ประเทศ /prà tʰêːt̚/ "country"

• K. ㅈ: initial 잠 /t͡ɕam/ "sleep" vs. final 낮 /nat̚/ "daytime"
• T. จ:  initial เจ็ด /t͡ɕèt̚/ "seven" vs. final ปีศาจ /piː sàːt̚/ "ghost"

• K. ㅊ: initial 창문 /t͡ɕʰaŋ mun/ "window" vs. final 꽃 /k͈ot̚/ "flower"
• T. ช: initial ช้าง /t͡ɕʰáːŋ/ "elephant" vs. final ธวัช /tʰá wát̚/ "flag"

Loss of "palatal" n at the beginning of syllables

Except in slang and recent loanwords, Modern Korean forbids word-initial ㄴ when followed by the vowel i or semivowel y. For example, the word for "teeth" used to be written and pronounced 니 (ni), but the ㄴ has been dropped: the word is now written and pronounced 이 (i).

Similarly, Thai has a letter (ญ) that used to be pronounced like the Spanish ñ. However, the nasal quality of this sound has been lost at the beginning of syllables, and is now pronounced like y. For example, the word หญิง "woman" is pronounced /jǐŋ/.

At the end of syllables, ญ has retained its nasal quality while losing its palatal quality to become an n sound, as in the word เจริญ "to prosper," pronounced /t͡ɕà rɤːn/. 

As a result, both Korean and Thai now have an underlying initial nasal sound whose only trace is an initial palatal sound (i or y), despite this same sound being fully present as n at the end of syllables. 

Multiple final consonants

Syllables in Korean and Thai can only end in one consonant max. Some words are written with two consonants at the end, but only one of them is pronounced. However, if another syllable is attached to the end of these words, the silent consonant resurfaces and is pronounced in that following syllable. In Korean, this only happens if the following syllable starts with a vowel.

• K: 값 /kap̚/ "price" (written kaps) + 이 /i/ -> 값이 /kap̚ ɕi/ "price (subject)"
  
• T: จักร /t͡ɕàk̚/ "wheel" (written jakr) + ยาน /jaːn/ -> จักรยาน /t͡ɕàk̚ kra jaːn/ "bicycle"

Variation between r/l and n

In Korean, r and l are represented by the same letter (ㄹ) and are considered allophones of the same sound, while in Thai, they are two distinct sounds. Despite this difference, in both languages, the  

r/l sounds may sound like n in certain positions. 

In Korean, this occurs in Sino-Korean words that should technically, due to their etymology, begin with ㄹ, but are written and pronounced as ㄴ (n) instead. Additionally, when ㄹ follows certain consonants, it is pronounced like n even though it is still written ㄹ.

• 勞動 "labor" -> 로동 (still written and pronounced as rodong in North Korea) -> 노동 (nodong in South Korea) 
• 心理 "mentality" -> 심리 (written shimri) but pronounced 심니 (shimni)

In Thai, this variation occurs at the end of a syllable instead of the beginning.

• ร (r): รัก /rák̚/ "love" vs. อาหาร /aː hǎːn/ "food"
• ล (l): ลิง /liŋ/ "monkey" vs. ตาล /taːn/ "palm tree" 

Conclusion

Despite being very different languages, Korean and Thai share quite a few phonological processes. Please let me know if there are any mistakes in this post.