A story of "ฤ"

ฤ ( รึ ru; an independent Thai vowel adopted from Sanskrit; unicode 0E24) is an interesting vowel. Why?

There are not many Thai words spelled with ฤ :
ฤกษ์ ฤดู ฤทธิ์ ฤๅ ฤๅษี อังกฤษ (I am sure you know more than these. Can you help make a complete list? Please? ;-)

How do we read ฤกษ์ ?
How we we read ฤดู ?
...

Can we see now why the vowel ฤ is interesting?
Why don't we read อังกฤษ as อัง กรึด or อัง เกริด ?

What (grammar) rule tells us to read อังกฤษ as อัง กริด ? Can anyone explain?

Many Thai language students have asked me the same questions I asked my Grade 1 teachers many many years ago. Before I get to the questions, let me repeat the basic. 

Letters in The Thai alphabet are of some 5 types:
1) vowel (สระ; 21 letters 32 sounds),
2) consonant (พยัญชนะ; 21 sounds, 44 letters),
3) tone mark (วรรณยุกต์; 4 letters, 5 sounds), and
4) silencer (การันต์ or ทัณทฆาต ; 1 letter, 0 sound -- to silence the letter(s)
5) sign (เครื่องหมาย เช่น ๆ ฯ ... please help me fill this list ;-)

Thai words are just certain compositions of letters in the Thai alphabet. The composition is generally following a simple formula: Note "[...]" = may be present.

Head_Consonant + a Vowel [+ a tone mark] + Tail_Consonant* [+ a silencer or a sign]

So far everyone can smile and nod agreement, right? Next, we devide consonants into some 3 groups:
1) middle tone (อักษรกลาง; 9 letters: ก จ ด ...)
2) high tone (อักษรสูง; 11 letters: ...)
3) low tone (อักษรต่ำ; ...) <*Some may subdivide this group into ต่ำคู่ and ต่ำเดี่ยว>

Vowels are divided into "short" and "long" groups.

Now we have "reading" rules:
r1) any middle tone consonant + any vowel ==> middle tone sound
r2) any low tone consonant + any short vowel ==> high tone sound
r3) any low tone consonant + any long vowel ==> low tone sound
r4) any high tone consonant + any short vowel ==> low tone sound
r5) any high tone consonant + any long vowel ==> high tone sound
...
There are many more rules for reading with tone marks, but we won't go into them.

Can you guess what my questions were (or are -- still)?

Why don't we have simpler rules like r1 for any high-tone or low-tone with short-vowel or long vowel that is :

r1*) any (middle, high, low) consonant + any vowel ==> (middle, high, low) sound

This way 

กะ reads กะ     กา reads กา
ขะ reads (คะ)* ขา reads ขา
คะ reads (ขะ)* คา reads คา

To put it another way เขมร reads คะเหมน สุข reads ซุก สะบาย reads ซะบาย...
คะ reads ขะ หะ reads ฮะ ฉะ reads ชะ ชะ reads ฉะ...

Did you say this is confusing? Yes, only after we have been "trained to read that way". We don't know when, where and why these twisted reading rules come about. (Please someone tell me history or reasons so I can learn more.) To me when I was a young Thai learner and to many Thai beginners today, these rules are just "quirks" that we have to learn to accept. Like we have have to accept -- words are bunched together (without a space between them or rigid grammar rules) and many adopted words and letters from other languages.

I have been looking at making "computers" read or speak Thai, write Thai (dictation) from speech, and in simple ways learn to understand Thai. These are "things" that make me (and computers) work harder and because of that we are being delayed by these excess weight (unnecessary rules and no rules when some are needed).

If you were a master of Thai language, what is your response? Can we talk more?