Thai is a tonal language with five tones: Mid, Low, Falling, High, and Rising. Meanings can change critically based on the tone, but Thais are fairly used to hearing foreigners mangle their language and can often work out the correct tone based on context. Try not to inflect your sentences: in particular, any questions should be pronounced as flat statements, without the rising intonation ("...yes?") typical to English questions.
The Thai written language is essentially alphabetic, but notoriously difficult to read due to a profusion of 44 consonants (many redundant), complicated tone and vowel signage around consonants and a complete lack of spaces between words.
Thai has a complicated set of vowels and diphthongs that distinguishes between vowel length (short and long) and vowel position (front and back). In Thai script, vowel signs are always written around consonants and the letter ก (k) is used here to demonstrate. This list follows the Royal Thai General System of Transcription (except that some long vowels are doubled).
like 'a' in "car" (short vowel)
like 'a' in "father" (longer than "a")
like 'a' in "man" (short vowel: "แกะ")
like 'e' in "bed" (short vowel: "เกะ")
like 'y' in "greedy"
like 'ee' in "see" (longer than "i")
like 'o' in "torn" (short vowel: "เกาะ")
like 'oa' in "moan" (short vowel: "โกะ")
like 'i' in "sir" (short vowel: "เกอะ")
like 'oo' in "hoop"
like 'ue' in "blue" (longer than "u")
frontal version of "u" (akin to German "ü", French "du", not found in English) (short vowel: "กึ")
like 'um' in "dummy"
like 'i' in "kind"
like 'eer' in "beer" (but don't pronounce "r")
similar to 'ou' in "tour" (but don't pronounce "r")
Thai distinguishes between aspirated ("with a puff of air") and unaspirated ("without a puff of air") consonants. Unaspirated consonants exist in English too, but never alone: compare the sound of 'p' in "pot" (aspirated) and "spot" (unaspirated). Many English speakers find it helpful to pronounce an imperceptible little "m" in front to 'stop' the puff.
In Thai romanized with the Royal Thai General System (used on Wikitravel), the distinction is usually represented by writing aspirated consonants with "h" and unaspirated ones without it. In particular, "ph" represents a hard aspirated 'p' and not a soft 'f', and Phuket is thus pronounced "Poo-ket". Likewise, "th" is a hard aspirated 't' and hence Thailand is pronounced "Tie-land".
Other systems of romanization may use 'bp', 'dt' and 'g' for the unaspirated sounds, and 'p', 't', and 'k' for the aspirated sounds. This is not used on Wikitravel.
like 'b' in "bed"
not used in Wikitravel, but in other romanizations may represent unaspirated 'p'
ch ฉ ช ฌ
like 'ch' in "chop"
d ฎ ด
like 'd' in "dog"
not used in Wikitravel, but in other romanizations may represent unaspirated 't'
f ฝ ฟ
like 'ph' in "phone"
not used in Wikitravel, but in other romanizations may represent unaspirated 'k'
h ห ฮ
like 'h' in "help"
like 'dg' in "edge"
like 'k' in "skate" (unaspirated)
kh ข ฃ ค ฅ ฆ
like 'c' in "cat" (aspirated)
l ล ฦ ฬ
like 'l' in "love"
like 'm' in "mother"
n ณ น
like 'n' in "nice"
like 'ng' in "sing", can also be used at the beginning of words
like 'p' in "spit" (unaspirated)
ph ผ พ ภ
like 'p' in "pig" (aspirated)
r ร ฤ
very light 'r', often pronounced as 'l' or omitted entirely
s ซ ศ ษ ส
like 'ss' in "hiss",
t ฏ ต
like 't' in "stab"
th ฐ ฑ ฒ ถ ท ธ
like 't' in "top"
not used in Wikitravel, but in other romanizations may represent 'w'
Note that that the polite suffix ครับ khráp (for men) and ค่ะ khâ (for women) can and should be attached to all phrases when talking with strangers. The suffix depends solely on the speaker's gender. Also note that the pronoun for "I" is ผม phǒm for men and ดิฉัน di-chǎn for women.
Many a visitor has suggested, perhaps slightly tongue in cheek, that ไม่เป็นไร mai pen rai should be the national motto of Thailand. Literally "is no problem", this is most commonly used where an English speaker would say "OK", "no problem" or "never mind". But watch out, as this can also be used in the negative sense: a mai pen rai in response to a complaint about missing your bus or being overcharged now means "it's not my problem"!
Thai numbering is quite regular and speakers of Cantonese will find many quite familiar. Note that in casual speech it is common to drop the "sip" from numbers over twenty, eg. 23 is yii-saam instead of yii-sip-saam.
Thai has its own set of numerals, shown below, but these are used quite rarely — the major exception being sites with double pricing for Thais and foreigners, the Thai price being often disguised with Thai numbers. Being able to read the Thai price just might get you in at the Thai rate.
There are no less than three systems for telling time in Thailand.
The easiest of the three is 24-hour official clock, encountered primarily in bus and railway schedules. To create an official time, simply affix naalikaa to the number of hours, so that e.g. kao naalikaa is 9 AM (0900) and sip-saam naalikaa is 1 PM (1300).
Things get a little more difficult in the 12-hour common clock. As in the West, the number of the hour runs from 1 to 12, but instead of just AM and PM, the day is divided into four sections (ตอน ton):
เช้า chao (morning), from 6 AM to noon
บ่าย baai (afternoon), from noon to 4 PM
เย็น yen (evening), from 4 PM to 6 PM
คืน kham (night), from 6 PM to 11 PM
A 12-hour time is thus composed from the hour, the word mong and the correct ton. As exceptions, the word baai comes before mong (not after); 1 PM is just baai moong with no number; and there are special words for noon and midnight. Some examples:
00 AM : ่ตีหนึ่ง (tii nueng')
00 AM : ตีสอง (tii song)
00 AM : ตีสาม (tii säam)
00 AM : ตีสี่ (tii sìi)
00 AM : ตีห้า (tii hâ)
00 AM : หกโมงเช้า (hòk mong cháo)
00 AM : เจ็ดโมงเช้า (jèt mong cháo)
00 AM : แปดโมงเช้า (paet mong cháo)
00 AM : เก้าโมงเช้า (kao mong cháo)
00 AM : สิบโมงเช้า (sip mong cháo)
00 AM : สิบเอ็ดโมงเช้า (sip-e mong cháo)
เที่ยงวัน (thîang wan)
00 PM : บ่ายโมง (bàai mong)
00 PM : บ่ายสองโมง (bàai song mong)
00 PM : บ่ายสามโมง (bàai säam mong)
00 PM : สี่โมงเย็น (sìi mong yen')
00 PM : ห้าโมงเย็น (hâa mong yen')
00 PM : หกโมงเย็น (hòk' mong yen')
00 PM : หนึ่งทุ่ม (nueng' thum')
00 PM : สองทุ่ม (song thum')
00 PM : สามทุ่ม (säam thum)'
00 PM : สี่ทุ่ม (sìi thum')
00 PM : ห้าทุ่ม (hâ thum')
00 midnight : เที่ยงคืน, สองยาม (Thîang khuen, song yaam)