The Tibetan language is spoken over a wide area of the
Himalayas, roughly corresponding to the furthest extent of the historical Tibetan empire. It covers not just the
Tibet Autonomous Region but other adjoining areas of China and other countries, of which the most prominent Tibetan areas are
Bhutan, the
Sherpas of Nepal,
Ladakh in Indian Kashmir, and
Baltistan in Pakistani Kashmir.
In such a compass there is a great range of dialects, with decreasing mututal intelligibility depending on distance. Modern Bhutan is promoting one of its own varieties as a national language called Dzongkha. There is also a standard Ladakhi language based on the dialect of Leh. The Lhasa variety of Central Tibetan is often used as the lingua franca of all the Tibetan-speaking areas.
What really unites the dialects is the fact that they use the same written form, which may be called Classical Tibetan. From about the seventh and eighth centuries Buddhist literature was translated from Sanskrit into Tibetan and formed the basis of a rich indigenous literature.
The classical language is characterized by a very heavy use of initial consonant clusters, and a lot of final consonants. Modern dialects can be classified by how archaic they are with respect to these phonological aspects. Lhasa Tibetan is non-archaic, and such dialects in losing some of their consonants have gained a greater variety in vowel sounds, including length, tone, and nasalization. Both stress and vowel harmony affect the pronunciations of vowels a lot.
(My crude rule of thumb is to strip off consonants from the outside until you can pronounce it: so turn brdzags into zag or even za. This isn't nearly right in all cases, but it'll be roughly right perhaps half the time. See the website below for some of the many "special rules" that govern this process.)
The native name for Tibet is written Bod, Lhasa spoken Pö, and the language is Bod-skad or Pöge. The capital Lhasa is now pronounced Lhesa, and has a voiceless L or lateral fricative.
Further afield, Tibetan is related to Burmese and to many minor languages of Myanmar and of neighbouring parts of India and China. These are grouped as the Tibeto-Burman family. Since the diversity is greatest in Myanmar and the Tibetan dialects have not had time to split into fully independent languages, it is probable that the Tibetans are relatively recent newcomers into Tibet, and the language might have been spread by the growth of the empire from the seventh century onward. The main Chinese languages form a more distant branch related to Tibeto-Burman, and the largest family identifiable is called Sino-Tibetan.
As an example of distance of relatedness, the Tibetan for 'one' and 'two' are written gcig and gnyis, Lhasa spoken chi and nyi. The Mandarin Chinese are yi and èr, the Sino-Japanese are iti and ni, and the Cantonese are yat and i. These Chinese forms show considerable wear and tear from their Ancient Chinese reconstructed ancestors yet and nzhi; but these are still simple compared to the Tibetan. In the intermediate Burmese they are tach and hnach.
Grammatical features. Tibetan noun phrases are head-initial, that is adjectives and other qualifiers and case markings follow the noun. It is SOV, that is verbs come last in their clause. Verbs may have several stems, present, past, future, and imperative. In the Lhasa dialect there is very little phonetic difference between them, usually none, but in written Tibetan they come in a complicated array of conjugations, with vowel ablaut as well as variation in the surrounding consonants: the past usually has the prefix b-, but it is difficult to make any other wide generalizations.
Inflected verbs consist of stems followed by tense/aspect particles and an auxiliary. These express a number of shades: subjective or objective, certain or doubtful or hearsay, intentional or unintentional.
Many words have honorific forms, sometimes etymologically unrelated but often formed by various prefixes on the plain form: these denote respect for the person referred to by the word (or its owner or subject); there is also a small class of respectful words for when respect is paid to the addressee, regardless of whether they figure in the sentence.
Denwood, P. (1999) Tibetan, John Benjamins
Special rules for phonetic transcription: http://iris.lib.virginia.edu/tibet/xml/showEssay.php?xml=/collections/langling/THDL_phonetics.xml&l=d1e671
Obviously my transcriptions here have to be inexact. If I wanted to give more detail about sound I'd have to use a complicated variety of phonetic alphabet.