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Unicode Transliteration Guidelines
Introduction
Transliteration is the general process of converting characters from one script to another, where the result is roughly phonetic for languages in the target script. For example, "Phobos" and "Deimos" are transliterations of Greek mythological "Φόβος" and "Δεῖμος" into Latin letters, used to name the moons of Mars. Transliteration is not translation. Rather, transliteration is the conversion of letters from one script to another without translating the underlying words. The following shows a sample of transliteration systems:
While an English speaker may not recognize that the Japanese word kyanpasu is equivalent to the English word campus, the word kyanpasu is still far easier to recognize and interpret than if the letters were left in the original script. There are several situations where this transliteration is especially useful, such as the following. See the sidebar for examples.
The term transliteration is sometimes given a narrow meaning, implying that the transformation is reversible (sometimes called lossless). In CLDR this is not the case; the term transliteration is interpreted broadly to mean both reversible and non-reversible transforms of text. (Note that even if theoretically a transliteration system is supposed to be reversible, in source standards it is often not specified in sufficient detail in the edge cases to actually be reversible.) A non-reversible transliteration is often called a transcription, or called a lossy or ambiguous transcription. Note that reversibility is generally only in one direction, so for native to Latin a transliteration may be reversible, but not the contrary. For example, Hangul is reversible, in that any Hangul to Latin to Hangul should provide the same Hangul as the input. Thus we have the following:
However, for completeness, many Latin characters have fallbacks. This means that more than one Latin character may map to the same Hangul. Thus from Latin we don't have reversibility, because two different Latin source strings round-trip back to the same Latin string.
Transliteration can also be used to convert unfamiliar letters within the same script, such as converting Icelandic THORN (þ) to th. These are not typically reversible.
VariantsThere are many systems for transliteration between languages: the same text can be transliterated in many different ways. For example, for the Greek example above, the transliteration is classical, while the UNGEGN alternate has different correspondences, such as φ → f instead of φ → ph. CLDR provides for generic mappings from script to script (such as Cyrillic-Latin), and also language-specific variants (Russian-French, or Serbian-German). There can also be semi-generic mappings, such as Russian-Latin or Cyrillic-French. These can be referred to, respectively, as script transliterations, language-specific transliterations, or script-language transliterations. Transliterations from other scripts to Latin are also called Romanizations. Even within particular languages, there can be variant systems according to different authorities, or even varying across time (if the authority for a system changes its recommendation). The canonical identifier that CLDR uses for these has the form:
The source (and target) can be a language or script, either using the English name or a locale code. The variant should specify the authority for the system, and if necessary for disambiguation, the year. For example, the identifier for the Russian to Latin transliteration according to the UNGEGN system would be:
If there were multiple versions of these over time, the variant would be, say, UNGEGN2006. The assumption is that implementations will allow the use of fallbacks, if the exact transliteration specified is unavailable. For example, the following would be the fallback chain for the identifier Russian-English/UNGEGN. This is similar to the Lookup Fallback Pattern used in BCP 47 Tags for Identifying Languages, except that it uses a "stepladder approach" to progressively handle the fallback among source, target, and variant, with priorities being the target, source, and variant, in that order.
GuidelinesThere are a number of generally desirable guidelines for script transliterations. These guidelines are rarely satisfied simultaneously, so constructing a reasonable transliteration is always a process of balancing different requirements. These requirements are most important for people who are building transliterations, but are also useful as background information for users. The following lists the general guidelines for Unicode CLDR transliterations:
Some of these principles may not be achievable simultaneously; in particular, adherence to a standard system and reversibility. Often small changes in existing systems can be made to accommodate reversibility. However, where a particular system specifies a fundamentally non-reversible transliterations, those transliterations as represented in CLDR may not be reversible. AmbiguityIn transliteration, multiple characters may produce ambiguities (non-reversible mappings) unless the rules are carefully designed. For example, the Greek character PSI (ψ) maps to ps, but ps could also result from the sequence PI, SIGMA (πσ) since PI (π) maps to p and SIGMA (σ) maps to s. The Japanese transliteration standards provide a good mechanism for handling these kinds of ambiguities. Using the Japanese transliteration standards, whenever an ambiguous sequence in the target script does not result from a single letter, the transform uses an apostrophe to disambiguate it. For example, it uses that procedure to distinguish between man'ichi and manichi. Using this procedure, the Greek character PI SIGMA (πσ) maps to p's. This method is recommended for all script transliteration methods, although sometimes the character may vary: for example, "-" is used in Korean.
A second problem is that some characters in a target script are not normally found outside of certain contexts. For example, the small Japanese "ya" character, as in "kya" (キャ), is not normally found in isolation. To handle such characters, the Unicode transliterations currently use different conventions.
For the default script transforms, the goal is to have unambiguous mappings, with variants for any common use mappings that are ambiguous (non-reversible). In some cases, however, case may not be preserved. For example,
The following shows Greek text that is mapped to fully reversible Latin:
If the user wants a version without certain accents, then CLDR's chaining rules can be used to remove the accents. For example, the following transliterates to Latin but removes the macron accents on the long vowels.
The above chaining rules, separated by semi-colons, perform the following commands in order:
The following transliterates to Latin but removes all accents. Note that the only change is to expand the filter for the remove command.
PronunciationStandard transliteration methods often do not follow the pronunciation rules of any particular language in the target script. For example, the Japanese Hepburn system uses a "j" that has the English phonetic value (as opposed to French, German, or Spanish), but uses vowels that do not have the standard English sounds. A transliteration method might also require some special knowledge to have the correct pronunciation. For example, in the Japanese kunrei-siki system, "ti" is pronounced as English "chee". This is similar to situations where there are different languages within the same script. For example, knowing that the word Gewalt comes from German allows a knowledgeable reader to pronounce the "w" as a "v". When encountering a foreign word like jawa, there is little assurance how it is to be pronounced even when it is not a transliteration (it is just from /span>another Latin-script language). The j could be pronounced (for an English speaker) as in jump, or Junker, or jour; and so on. Transcriptions are only roughly phonetic, and only so when the specific pronunciation rules are understood. The pronunciation of the characters in the original script may also be influenced by context, which may be particularly misleading in transliteration. For, in the Bengali নিঃশব, transliterated as niḥśaba, the visarga ḥ is not pronounced itself (whereas elsewhere it may be) but lengthens the ś sound, and the final inherent a is pronounced (whereas it commonly is not), and the two inherent a's are pronounced as ɔ and ô, respectively. In some cases, transliteration may be heavily influenced by tradition. For example, the modern Greek letter beta (β) sounds like a "v", but a transliteration may use a b (as in biology). In that case, the user would need to know that a "b" in the transliterated word corresponded to beta (β) and is to be pronounced as a v in modern Greek. Letters may also be transliterated differently according to their context to make the pronunciation more predictable. For example, since the Greek sequence GAMMA GAMMA (γγ) is pronounced as ng, the first GAMMA can be transcribed as an "n" in that context. Similarly, the transliteration can give other guidance to the pronunciation in the source language, for example, using "n" or "m" for the same Japanese character (ん) depending on context, even though there is no distinction in the source script. In general, predictability means that when transliterating Latin script to other scripts using reversible transliterations, English text will not produce phonetic results. This is because the pronunciation of English cannot be predicted easily from the letters in a word: e.g. grove, move, and love all end with "ove", but are pronounced very differently. CautionsReversibility may require modifications of traditional transcription methods. For example, there are two standard methods for transliterating Japanese katakana and hiragana into Latin letters. The kunrei-siki method is unambiguous. The Hepburn method can be more easily pronounced by foreigners but is ambiguous. In the Hepburn method, both ZI (ジ) and DI (ヂ) are represented by "ji" and both ZU (ズ) and DU (ヅ) are represented by "zu". A slightly amended version of Hepburn, that uses "dji" for DI and "dzu" for DU, is unambiguous. When a sequence of two letters map to one, case mappings (uppercase and lowercase) must be handled carefully to ensure reversibility. For cased scripts, the two letters may need to have different cases, depending on the next letter. For example, the Greek letter PHI (Φ) maps to PH in Latin, but Φο maps to Pho, and not to PHo. Some scripts have characters that take on different shapes depending on their context. Usually, this is done at the display level (such as with Arabic) and does not require special transliteration support. However, in a few cases this is represented with different character codes, such as in Greek and Hebrew. For example, a Greek SIGMA is written in a final form (ς) at the end of words, and a non-final form (σ) in other locations. This also requires the transform to map different characters based on the context. Another thing to look out for when dealing with cased scripts is that some of the characters in the target script may not be able to represent case distinctions, such as some of the IPA characters in the Latin script. It is useful for the reverse mapping to be complete so that arbitrary strings in the target script can be reasonably mapped back to the source script. Complete reverse mapping makes it much easier to do mechanical quality checks and so on. For example, even though the letter "q" might not be necessary in a transliteration of Greek, it can be mapped to a KAPPA (κ). Such reverse mappings will not, in general, be unambiguous. Available TransliterationsCurrently Unicode CLDR offers Romanizations for certain scripts, plus transliterations between the Indic scripts (excluding Urdu). Additional script transliterations will be added in the future. Except where otherwise noted, all of these systems are designed to be reversible. For bicameral scripts (those with uppercase and lowercase), however, case may not be completely preserved. The transliterations are also designed to be complete for any sequence of the Latin letters a-z. A fallback is used for a letter that is not covered by the transliteration, and default letters may be inserted as required. For example, in the Hangul transliteration, rink → 린크 → linkeu. That is, "r" is mapped to the closest other letter, and a default vowel is inserted at the end (since "nk" cannot end a syllable). Preliminary charts are available for the available transliterations. Be sure to read the known issues described there. KoreanThere are many Romanizations of Korean. The default transliteration in Unicode CLDR follows the Korean Ministry of Culture & Tourism Transliteration regulations (see also English summary). There is an optional clause 8 variant for reversibility:
There are a number of cases where this Romanization may be ambiguous, because sometimes multiple Latin letters map to a single entity (jamo) in Hangul. This happens with vowels and consonants, the latter being slightly more complicated because there are both initial and final consonants:
CLDR uses the following rules for disambiguation of the possible boundaries between letters, in order. The first rule comes from Clause 8.
If there is a single consonant between vowels, then Rule #1 will group it with the following vowel if there is one (this is the same as the first part of Clause 8). If there is a sequence of four consonants between vowels, then there is only one possible break (with well-formed text). So the only ambiguities lie with two or three consonants between vowels, where there are possible multi-character consonants involved. Even there, in most cases the resolution is simple, because there isn't a possible multi-character consonant in the case of two, or two possible multi-character consonants in the case of 3. For example, in the following cases, the left side is unambiguous:
There are a relatively small number of possible ambiguities, listed below using "a" as a sample vowel.
* There is one other known bug in CLDR 1.5.1, where "ch" transliterates incorrectly in the degenerate case — when not followed by a vowel. For vowel sequences, the situation is simpler. Only Rule #3 applies, so aeo = ae-o → 애오. JapaneseThe default transliteration for Japanese uses the a slight variant of the Hepburn system. With Hepburn system, both ZI (ジ) and DI (ヂ) are represented by "ji" and both ZU (ズ) and DU (ヅ) are represented by "zu". This is amended slightly for reversibility by using "dji" for DI and "dzu" for DU. GreekThe default transliteration uses a standard transcription for Greek which is aimed at preserving etymology. The ISO 843 variant includes following differences:
* before γ, κ, ξ, χ CyrillicCyrillic generally follows ISO 9 for the base Cyrillic set. There are tentative plans to add extended Cyrillic characters in the future, plus variants for GOST and other national standards. IndicTransliteration of Indic scripts follows the ISO 15919 Transliteration of Devanagari and related Indic scripts into Latin characters. Internally, all Indic scripts are transliterated by converting first to an internal form, called Inter-Indic, then from Inter-Indic to the target script. Inter-Indic thus provides a pivot between the different scripts, and contains a superset of correspondences for all of them. ISO 15919 differs from ISCII 91 in application of diacritics for certain characters. These differences are shown in the following example (illustrated with Devanagari, although the same principles apply to the other Indic scripts):
Transliteration rules from Indic to Latin are reversible with the exception of the ZWJ and ZWNJ used to request explicit rendering effects. For example:
Transliteration between Indic scripts are roundtrip where there are corresponding letters. Otherwise, there may be fallbacks. There are two particular instances where transliterations may produce unexpected results: (1) where the final vowel is suppressed in speech, and (2) with the transliteration of 'c'. For example:
OthersUnicode CLDR provides other transliterations based on the U.S. Board on Geographic Names (BGN) transliterations. These are currently unidirectional — to Latin only. The goal is to make them bidirectional in future versions of CLDR. Other transliterations are generally based on the UNGEGN: Working Group on Romanization Systems transliterations. These systems are in wider actual implementation than most ISO standardized transliterations, and are published freely available on the web (http://www.eki.ee/wgrs/) and thus easily accessible to all. The UNGEGN also has good documentation. For example, the UNGEGN Arabic Tables not only presents the UN system, but compares it with the BGN/PCGN 1956 system, the I.G.N. System 1973, ISO 233:1984, the royal Jordanian Geographic Centre System, and the Survey of Egypt System. Submitting TransliterationsIf you are interested in providing transliterations for one or more scripts, file an initial bug report at Locale Bugs. The initial bug should contain the scripts and or languages involved, and the system being followed (with a link to a full description of the proposed transliteration system), and a brief example. The proposed data can also be in that bug, or be added in a Reply to that bug. You can also file a bug in Locale Bugs if you find a problem in an existing transliteration. For submission to CLDR, the data needs to supplied in the correct XML format, and should follow an accepted standard. It is best if the results are tested using the ICU Transform Demo first, since if the data doesn't validate it would not be accepted into CLDR. As mentioned above, even if a transliteration is only used in certain countries or contexts CLDR can provide for them with different variant tags. The format for rules is specified in Transform_Rules. The XML format is just a series of rules and comments. For comparison, you can see what is currently in CLDR in the transforms folder online. For example, see Hebrew-Latin.xml. More InformationFor more information, see:
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