Lü (or Lue) is a Southwestern Tai language spoken mainly in Yunnan province, China.
Among the Tai-Kadai languages of China, Lü stands out because it has a unique script, New Tai Lue, that appears on all street signs and store fronts in the area around Xishuangbanna, down to the border with Laos.
In fact, Lü is written in many scripts. New Tai Lue script is a reformed script invented by scholars in China after the communist revolution. The traditional Tai Tham script is still in use in Thailand and Laos. The inauthentic Thai and Lao scripts are also used for writing the language when one confronts the limitation of a system. Wiktionary chooses the New Tai Lue script for main entries and the Tai Tham script for alternative forms. The Thai and Lao scripts are not accepted.
In the New Tai Lue script, the language can optionally be written with a space separating each syllable rather than each word. (This is an uncommon orthographic property shared with Vietnamese when written in the Latin script, Quốc Ngữ.)
In Unicode, the New Tai Lue script (U+1980 to U+19DF) was originally encoded in logical order, much like the Burmese and Khmer scripts. But in Unicode version 8 it was changed to visual order, e.g. a front vowel must be input before a consonant, much like Thai and Lao due to the majority of extant digital documents being produced in visual order. This has resulted in some inconsistent behaviour as on February 2016.
There are at least one Chinese-Lü and one English-Lü dictionary published in recent years. The former is available to buy online via various internet booksellers in China but many are sold out due to a low print run. The latter is far more expensive but can be purchased from Monument Books in Pakse in Laos.
There is an official Xishuangbanna news site with a version in the New Tai Lue script and a version in the traditional script. (Caution: some words might be nonstandardly spelled.)
Vocabulary is dominated by borrowings from Chinese for anything that might be considered a modern or foreign concept. Core vocabulary is a bit closer to Lao than to Thai but there are phonological differences between Lü and both of those languages.
In Yunnan there are Dai restaurants which can often be recognized by an architectural style resembling that of Thailand and Laos and often feature a golden peacock motif.
There are several other Dai languages spoken in China and several other Tai-Kadai languages which are more distantly related and include Zhuang and Bouyei.