Yiddish is a Germanic language derived from High German with influence from Hebrew, Aramaic, Slavic languages, and Romance languages. It is widely spoken by Jews of European origin throughout Europe, North America, Brazil and Argentina. The language is written in the Hebrew script, but there is significant variation in orthographic styles, largely because the language itself has no official status so there is no authoritative governing body to regulate the orthography. In the late 19th and early 20th centuries Yiddish spelling generally followed German orthography as closely as possible. In 1936, the Yiddish Scientific Institute (YIVO) and Central Yiddish School Organisation published the 'Rules of Yiddish orthography' which has provided the most widely accepted standard in the absence of any government-approved publication.
In most Yiddish texts, words of Hebrew and Aramaic origin are generally written as they are in their original language. Exceptions to this have included publications by Soviet Yiddish authors, for whom the Semitic spelling may have had undesirable political or religious connotations. As a result, letters which occur only in words of Semitic origin are not found in Soviet Yiddish orthographies. Yiddish words may combine Semitic and non-Semitic roots and affixes; some spelling styles separate these with an apostrophe.
Dialect differences in spoken Yiddish are mostly found in their vocalic systems. The YIVO orthography fully represents vowels, but cannot accurately reflect all of the dialectal variation which is present in speech. Only three vowel letters can occur at the start of a word, representing [a], [o], and [e]. To write a word which starts with one of the other vowels, for example ['ɛjbɪk] 'eternal', a silent alef character is written as a prefix. Generally, when a word of this sort is itself prefixed by another morpheme, for example [fɑr'ɛjbɪkŋ] 'immortalize', the silent alef is still written before the 'offending' vowel, even though it is now in the middle of the word.
Stress is distinctive in Yiddish - that is, two words comprised of the same phones may have different meanings depending on their stress patterns - but it is not represented in the writing.
Yiddish writing uses four ligatures which are not needed for writing Hebrew.
Howard I Aronson "Yiddish" pp735-741 The World's Writing Systems