With the help of a two Thai friends I have put together a few thai love phrases for those of you falling in love with a Thai woman or man. I have translated the words as my Thai friends would write them in English, and because some of the words often sound different when spoken by Thais, I have added notes to help you with translation.
The Thai language has 5 tones, but for this simple exercise and to save confusion I have simply instructed when to go up and down in tone for certain words. This will almost guarantee Thais will understand what you are trying to say. 
Remember, each of these phrases/questions should have the male/female pleasantry attached to the end. If you are a man say “Khrup”, often heard as “khup”, and sounds like “cup”. If you are a lady say “Ka” at the end of each sentence.
1. Let’s go to eat together – Pai taan khaao duai kan na.
(“Pai” sounds more like “by”/”buy”. “Khaao” sounds more like “cow” and goes up in tone. “Duai” goes up in tone. “Kan” sounds more like “gan”, and “na” goes up in tone).
2. Can I have your telephone number? – Khaw boe thohrasap khun dai mai?
(“Khaw” goes down in tone and sounds more like “cor”. “Boe” sounds more like “ber”. The “ra” in “thohrasap” goes up in tone and the “sap” goes down in tone. “Dai” goes up in tone and “mai” goes down in tone).
3. Can I call you? – Phom thoh haa khun dai mai? (use Chan with a downwards tone if you are a woman).
(“Haa” goes down in tone, “dai” up in tone and “mai” down in tone).
4. Take care – Duulae tua aeng duai na.
(This is a little more difficult. “Duulae” sounds more like “dulair”. “Tua” sounds more like “dua”. “Duai” goes up in tone, as does “na”).
5. You are beautiful – Khun suai jang loei.
(“Suai” has a downward tone that sounds like “suuway”).
6. You are handsome – Khun law.
(“Law” has a downward tone and is pronounced more like “lor” rather than “law”).
7. You have beautiful eyes – Taa khun suai.
(“Taa” sounds more like “dar” when spoken by Thais).
8. You have a beautiful/wonderful smile – Khun yim suai.
(“Yim” goes upwards in tone, “suai”, pronounced “sooway” goes downwards in tone).
9. I miss you – Khit thueng khun.
(“Khit” is pronnounced more like “kit”, and has a downward tone).
10. You are cute – Khun naa rak.
(“Naa” goes upward in tone, as does “rak”).
11. You are sexy – Khun duu seksee.
(“Duu” has a downward tone. “Seksee” sounds just like “sexy” but with the syllables held onto longer and an upward tone).
12. Can I call you? – Phom thoh haa khun dai mai?
(“Haa” goes downwards in tone, “dai” upwards and “mai” downwards).
13. I love you - Phom rak khun (If you are a man).
(“Phom” goes downwards in tone, as does “rak”).
I love you – Chan rak khun (If you are a woman).
(“Chan” goes downwards in tone, as does “rak”).
14. You are special – Khun ben con pised
(“Pised” is pronounced ”piss-ed”)
If you want to further impress your Thai girlfriend, wife or potential dates, then there are a few Thai language software programs on the market. I have tried a couple, the first was naff, but I won’t expose the name – just because I didn’t get on with it doesn’t mean someone else won’t, and I don’t want to slag off a product unnecessarily. The one I use now is ThaiPod101, which is a really professional program that has advanced my Thai very quickly. Alternatively, if you want to start with learning to write and read the Thai alphabet (the best place to start in my opinion) from home then have a read of this interview I did with the author of a popular book that teaches foreigners the Thai alphabet in a day.
If anyone has any other phrases to add or comments on translation please feel free to comment.

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Great little guide. Now I can be a bit more romantic in Thai
Brutus(Quote)
I know every romentic words speaks in thai pls mail me
Sanjay Kumar Batra(Quote)
Very interesting! thank you
Rahma(Quote)
Glad you enjoyed the phrases!
TheThailandLife(Quote)
Paiboon’s ThaiDict Android/iphone apps. I found that it is very helpful. It is on target 85-90% of the time. And each word has a native thai pronunciation. I do like their paiboon+ romanization guide. They really do a good job of trying to pronounce the words properly and make it foreigner-friendly to see the differences in pronunciations. Very difficult to do with just a regular english keypad.
They plan on coming out with a separate dictionary for slang/common thai phrases with native pronunciation, and they will incorporate them into the main dictionaries at no extra charge.
I keep wanting a hand-held guide that will have a few variations of “How old are you?” “What is your name?”, “Are you available later this evening for…”
Jon(Quote)
Thanks for the heads up on that dictionary. I will download it on the iPad. My Thai Phrases guide has some useful stuff for everyday usage. http://www.thaipod101.com/thai-phrases/
TheThailandLife(Quote)