Language reform

Language reform is a type of language planning. Language reforms make big changes to a language. These changes are usually done to make a language simpler to understand or to write. Sometimes changes are done to make the language purer; that is, to get rid of foreign parts of the language, or to get rid of parts of the language that are not grammatical.
Simplification makes the language easier to use. It tries to regularise spelling, vocabulary, and grammar. Purification makes the language similar to a version of the language that people think is more pure.
Sometimes language reforms were done to unite the people speaking the language. For this reason, many language reforms happened in 19th century Europe when there was a rise of nationalist movements.
Simplification
The most common form of language reform involves changing the orthography of words. This is known as spelling reform. The grammar of a language also may be changed to simplify inflection, syntax, vocabulary and word formation. English for example uses many different prefixes that mean the opposite of, like un-, in-/im-, a(n)-, de-. A language reform might suggest using only one prefix to mean the opposite of, for example un-. On top of this, there are words such as "good" and "bad" that roughly mean the opposite of each other, but would be better (in terms of simplicity) portrayed as "good" and "ungood", so the word "bad" is not part of the language anymore.
Another good example of what language simplification can do is the word flammable. Flammable means that something can catch fire easily. Originally the word was inflammable, from Latin inflammare - put something on fire. In- is also a prefix that can mean the opposite of, like with transparent, intransparent. Today most instructions use flammable rather than inflammable, in order not to confuse people that the in- in this case does not mean the opposite of.
Several major world languages have been subject to big spelling reforms: French (in the 16th, 18th, 19th, 20th, and 21st centuries), Spanish (in the 18th century), Portuguese (in 1910, in Portugal, and in 1946 and 1972, in Brazil), German (in 1901/02 and 1996/98) and Russian (in 1728 and 1919).
Purification
Some people feel that it is bad to change a language. They want to keep a language the way it is now, or they want to take back changes to the language that have been done earlier. Sometimes, purism can make a language more complex, because people add false etymologies:
iland became island (from the Latin insula. Island is actually a Germanic word, compare German Eiland)
ile became isle (also from insula)
Examples
Examples of language reforms are:
Chinese
(1920s) - replaced Classical Chinese with Vernacular Chinese as the standard written language.
Mandarin was chosen at a committee from several Chinese dialects.
(1950s PRC) - reformed the script used to write the standard language by introducing Simplified Chinese characters (later adopted by Singapore and Malaysia, but Traditional Chinese characters remain in use in Taiwan, Hong Kong, Macau, and various overseas Chinese communities). About 2,000 Chinese characters have been simplified, most of them being common characters in day-to-day life.
Czech (19th century) - The dictionary of Josef Jungmann contributed to the renewal of the vocabulary. In the 1840s the letter w became replaced by v.
Estonian (1910s/1920s) - reform movement led by Johannes Aavik and Johannes V. Veski renewed the vocabulary, borrowing a lot of roots from Finnish and other Uralic languages and even inventing some roots that do not exist anywhere.
French (most recent in 1990): Simpler plurals of composite words, some modifications to hyphenation, some changes to accents; The past participle of transitive verbs in combinations with laisser (let) is now invariable, it was changed to reflect feminine forms and plural forms beforehand.
German (1901/02) - unified the spelling system nationwide (first in Germany, with later adoption by other Germanophone countries). Further reforms were enacted more recently, in the German spelling reform of 1996.
Greek (1970s/1980s) - while the written "pure" language, the katharevusa was full of Old Greek words, the spoken "popular" language, the dhimotiki was not. After the fall of the military rule, a law was promulgated, making the latter become the written language as well. For example, on Greek coins, the plural of the currency was drachmai (katharevusa form) before and became drachmes (dhimotiki form) after 1982.
Hebrew (1920s) - Modern Hebrew was created from Ancient Hebrew by simplification of the grammar (especially of the syntax) according to Indo-European models, coinage of new words from Hebrew roots based on European models, and simplification of pronunciation rules.
Hungarian (late 18th and early 19th centuries) - more than ten thousand words were coined, out of which several thousand are still actively used today.
Irish (1940s) - spelling system greatly simplified e.g. Gaedheal became Gael, O Seigheadh became O Se.
Korean (1446, after division of Korea in 1945) - in the year 1446, King Sejong hired scholars to create a writing system that was both easy to learn and accurately represented the sounds of the Korean language. The alphabet he made is hangul. It was only used by common people until 1945. In North Korea, Kim Il-sung's government completely abolished hanja (Chinese characters used for the Korean language) and made hangul the only writing system of North Korea. Also, many Chinese loanwords (which was previously 60-70% of Korean vocabulary) were removed and replaced with native Korean words to purify the Korean language, although North Korea had also adopted some Russian loanwords due to its trade relations with the Soviet Union. In South Korea, hangul has largely replaced hanja, making it the main writing system in South Korea, although many South Koreans still know some hanja and write them on official documents like contracts and job applications. Hanja is usually used only for Chinese loanwords and homophones where the word's meaning isn't clear by context. Koreans are expected to know around 1,900 hanja today.
Norwegian (20th century) - as Norway became independent from Denmark (1814), Norwegian started to drift away from Danish. The reforms in 1907 and 1917 made Riksmaal the written standard Norwegian, renamed Bokmaal in 1929. Bokmaal and the more vernacular Nynorsk were made closer by a reform in 1938. Today both language forms are spoken: on Norwegian coins, the name of the country is alternately Norge (Bokmaal) and Noreg (Nynorsk).
Portuguese (20th century) - replaced a cumbersome traditional spelling system with a simplified one (asthma, for instance, became asma and phthysica became tisica).
Romanian (19th century) - replaced the Cyrillic alphabet with the Latin alphabet, deprecated hundreds of Slavic words in favor of Romance ones.
Somali (1970s) - with the assistance of Bogumil W. Andrzejewski, who started his linguistic work in Somalia in 1949, a Latin alphabet was elaborated, made compulsory in 1972 by strongman General Mohamed Siad Barre. Also the vocabulary was renewed; a lot of new words became coined from existing Somali roots.
Turkish (1930s) - language and writing system were reformed starting in the 1920s, to the point that the older language is called by a different name, Ottoman Turkish. The Ottoman alphabet was based on the Arabic alphabet, which was replaced in 1928 by the new, Latin-based Turkish alphabet. Loanwords of Persian and Arabic origin were dropped in favor of native Turkish words or new coinages based on Turkic roots.
Vietnamese (20th century) - during the French colonial rule, the classical vernacular script based on Chinese characters was replaced with the new Latin alphabet.