espeak-ng/docs/add_language.md

# Adding or Improving a Language

- [Considerations Before Preparation](#considerations-before-preparation)
  - [Language Tag](#language-tag)
  - [Language Family](#language-family)
  - [Accent (optional)](#accent-optional)
- [Configuration Files](#configuration-files)
  - [Makefile.am file](#makefileam-file)
  - [Phonemes file](#phonemes-file)
  - [Language File](#language-file)
  - [Phoneme Definition File](#phoneme-definition-file)
  - [Dictionary Files](#dictionary-files)
- [Program Code](#program-code)
- [Compiling Rules File for Debugging](#compiling-rules-file-for-debugging)
- [Improving a Language](#improving-a-language)

----------

## Considerations Before Preparation


Most of the work doesn't need any programming knowledge, but, to get immediate
feedback, by running and testing eSpeak,
you should be able to [build](../README.md#building) it.

You also have to understand the language main concepts, be aware of its features,
and have to have patience and attention to detail.
Wikipedia is a good source of basic phonetic information, e.g. about [vowels]
(http://en.wikipedia.org/wiki/Vowel) and [consonants](https://en.wikipedia.org/wiki/Consonant).

In many cases it should be fairly easy to add a rough implementation of
a new language, hopefully enough to be intelligible. After that it's a
gradual process of improvement.

### Language Tag

The language is identified using the
[BCP 47](https://en.wikipedia.org/wiki/IETF_language_tag) language tag.
The list of valid tags originate from various standards and have been combined
into the
[IANA Language Subtag Registry](http://www.iana.org/assignments/language-subtag-registry/language-subtag-registry).

These language tags are used to specify the language, such as:

*  `fr` (French) -- The [ISO 639-1](https://en.wikipedia.org/wiki/ISO_639-1)
   2-letter language code for the language.

   __NOTE:__ BCP 47 uses ISO 639-1 codes for languages that are allocated
   2-letter codes (e.g. using `en` instead of `eng`).

*  `yue` (Cantonese) -- The [ISO 639-3](https://en.wikipedia.org/wiki/ISO_639-3)
   3-letter language codes for the language.

*  `ta-Arab` (Tamil written in the Arabic alphabet) -- The
   [ISO 15924](https://en.wikipedia.org/wiki/ISO_15924) 4-letter script code.

   __NOTE:__ Where the script is the primary script for the language, the script
   tag should be omitted.

### Language Family

The languages are grouped by the closest language family the language belongs.
These language families are defined in
[ISO 639-5](https://en.wikipedia.org/wiki/ISO_639-5). See also Wikipedia's
[List of language families](https://en.wiktionary.org/wiki/Wiktionary:List_of_families)
for more details.

For example, the Celtic languages (Welsh, Irish Gaelic, Scottish Gaelic, etc.)
are listed under the `cel` language family code.

### Accent (optional)

If necessary, the language tags are also used to specify the accent or dialect of a language,
such as:

*  `es-419` (Spanish (Latin America)) -- The
   [UN M.49](https://en.wikipedia.org/wiki/UN_M.49) 3-number region codes.

*  `fr-CA` (French (Canada)) -- Using the
   [ISO 3166-2](https://en.wikipedia.org/wiki/ISO_3166-2) 2-letter region codes.

*  `en-GB-scotland` (English (Scotland)) -- This is using the BCP 47 variant
   tags.

*  `en-GB-x-rp` (English (Received Pronunciation)) -- This is using the
   [bcp47-extensions](https://raw.githubusercontent.com/espeak-ng/bcp47-data/master/bcp47-extensions)
   language tags for accents that cannot be described using the available
   BCP 47 language tags.

   __NOTE:__ If the accent you are trying to describe cannot be specified using
   the above system, raise an issue in the
   [bcp47-data](https://github.com/rhdunn/bcp47-data) project and a private use
   tag will be defined for that accent.

## Configuration Files

To add new language, you have to create or edit following files:

|path/file                     |action  |
|------------------------------|--------|
| Makefile.am                  |edit    |
| phsource/phonemes            |edit    |
| phsource/ph_french           |create  |
| dictsource/fr_list           |create  |
| dictsource/fr_rules          |create  |
| dictsource/fr_extra          |create (optional) |
| espeak-ng-data/lang/roa/fr   |create  |

where:

* __french__ is name of the newly created language
* __fr__ is the code of this language
* __roa__ is the family of this language


### Makefile.am File

`Makefile.am` is build configuration file.

Search for configuration of existing languages (e.g. English)
and add similar lines for your language in following sections.
E.g. for French:

	phsource/phonemes.stamp: \
	...
	  phsource/ph_french \
	...
	
	dictionaries: \
	...
	  espeak-ng-data/fr_dict \
	...
	
	fr: espeak-ng-data/fr_dict
	dictsource/fr_extra:
	  touch dictsource/fr_extra
	espeak-ng-data/fr_dict: src/espeak-ng phsource/phonemes.stamp dictsource/fr_list dictsource/fr_rules dictsource/fr_extra
	  cd dictsource && ESPEAK_DATA_PATH=$(PWD) LD_LIBRARY_PATH=../src:${LD_LIBRARY_PATH} ../src/espeak-ng --compile=fr && cd ..
	...

Note, that you don't need to add `fr_extra` reference in the last group, if your language doesn't have this file.

### Phonemes File

Open file `phsource/phonemes` and add following lines into it,
to make it call your new, e.g. `ph_french` file:

	...
	phonemetable fr base
	include ph_french
	...

### Language File

E.g. `espeak-ng-data/lang/roa/fr` is the language file for French.
This gives the language name and may set some options.

Each language needs a language file in `espeak-ng-data/lang` grouped by the
[language family](#language-family). The filename of the default voice for a
language should be the same as the language code (e.g. `fr` for French).

The simplest voice file would contain just 2 lines to give the language
name (from the
[IANA Language Subtag Registry](https://github.com/rhdunn/bcp47-data/blob/master/language-subtag-registry)
and language code, e.g.:

	name French
	language fr

This language code specifies which phoneme table and dictionary to use
(i.e. `phonemetable fr` and `espeak-ng-data/fr_dict`) to be used. If
needed, these can be overridden by `phonemes` and `dictionary`
attributes in the voice file. For example you may want to start the
implementation of a new language by using the phoneme table of an
existing language.

Details of the contents of language files are given in [Voices](voices.md).

### Phoneme Definition File

E.g. `phsource/ph_french` is the phoneme definition file for French.
This contains phoneme definitions for the vowels and consonants which the language uses.
Usually it will contain mostly vowels. Most consonants will be inherited from the
common phoneme definitions in the _master phoneme file_: `phsource/phonemes`.

You must first decide on the set of phonemes (vowel and consonant
sounds) for the language. These should be defined in a phoneme
definition file `ph_french`, where `ph_french` is the name of your
language. A reference to this file is then included at the end of the
master phoneme file, `phsource/phonemes`, e.g.:

	phonemetable fr base
	include ph_french

This example defines a phoneme table `fr` which inherits the
contents of phoneme table `base`. Its contents are found in the file
`ph_french`.

The `base` phoneme table contains definitions of a basic set of
consonants, and also some "control" phonemes such as stress marks and
pauses. These are defined in `phsource/phonemes`. The phoneme table
for a language will inherit these, or alternatively it may inherit the
phoneme table of another language which in turn inherits the `base`
phoneme table.

The phonemes file for the language defines those additional phonemes
which are not inherited (generally the vowels and diphthongs, plus any
additional consonants that are needed), or phonemes whose definitions
differ from the inherited version (eg. the redefinition of a consonant).

Details of phonemes files are given in [Phoneme Tables](phontab.md).

To build the phoneme files, run:

	espeak-ng --compile-phonemes

or:

	make phsource/phonemes.stamp

For many languages, the consonant phonemes which are already available
in eSpeak, together with the available vowel files which can be used to
define vowel phonemes, will be sufficient. At least for an initial
implementation.

### Dictionary Files

There are usually two dictionary files, e.g. for French:

  * `dictsource/fr_list`. This contains pronunciations for numbers, letter and
    symbol names, and words with exceptional pronunciations. It also gives
    attributes such as "unstressed" and "pause" to some common words.
    The `fr_list` file contains:

      * Pronunciations which exceptions to the rules in `fr_rules`, (e.g. foreign
        names).
      * Pronunciation of letter names, symbol names, and punctuation names.
      * Pronunciation of numbers.
      * Attributes for words. For example, common function words which should not
        be stressed, or conjunctions which should be preceded by a pause. 

  * `dictsource/fr_rules`. This contains the spelling-to-phoneme translation
     rules.

Details of the contents of the dictionary files are given in
[Dictionary](dictionary.md).

The `fr_rules` and `fr_list` files are compiled to produce the
`espeak-ng-data/fr_dict` file, which eSpeak uses when it is speaking.

Once the language's phonemes have been defined, then pronunciation
dictionary data can be produced in order to translate the language's
source text into phonemes. This consists of two source files:
`fr_rules` (the spelling to phoneme rules) and `fr_list` (an
exceptions list, and attributes of certain words). The corresponding
compiled data file is `espeak-ng-data/fr_dict` which is produced from
the `fr_rules` and `fr_list` sources by the command:

	espeak-ng --compile=fr

or by:

	make fr

## Program Code

The behaviour of the eSpeak program is controlled by various options
such as:

* Default rules for which syllable of a word has the main stress.
* Relative lengths and amplitude of vowels in stressed and unstressed syllables.
* Which intonation tunes to use.
* Rules for speaking numbers.

Most of these options can be set in the voice file in espeak-ng-data/lang folder (see [Voices](voices.md)).
However some advanced options may be needed to add in source code in the function `SelectTranslator()`
of the [tr_languages.c](https://github.com/espeak-ng/espeak-ng/blob/master/src/libespeak-ng/tr_languages.c)
file.

## Compiling Rules File for Debugging

When `espeak-ng` is invoked with `-X` parameter, it shows more detailed trace of 
chosen language rules for pronunciation. This trace can show line numbers also, 
if language is compiled with `--compile-debug` option.

To do this, go to `espeak-ng` project root folder, then:

	cd dictsource
	../src/espeak-ng --compile-debug=en

When invoked in following way:

	espeak-ng -ven -X "Test."

It will show:

	Translate 'test'
	  1  5965:  t [t]
	
	  1  2104:  e [E]
	
	  1  5725:  s [s]
	
	  1  5965:  t [t]
	
	 t'Est

## Improving a Language

Listen carefully to the eSpeak voice. Try to identify what sounds wrong
and what needs to be improved.

* Make the spelling-to-phoneme translation rules more accurate, including
  the position of stressed syllables within words. Some languages are easier
  than others. I expect most are easier than English.

* Improve the sounds of the phonemes. It may be that a phoneme should sound
  different depending on adjacent sounds, or whether it's at the start or the
  end of a word, between vowels, in a stressed or unstressed syllable, etc.
  This may consist of making small adjustments to vowel and diphthong quality
  or length, or adjusting the strength of consonants. Phoneme definitions can
  include conditional statements which can be used to change the sound of a
  phoneme depending on its environment. Bigger changes may be recording new or
  replacement consonant sounds, or may even need program code to implement new
  types of sounds.

* Some common words should be added to the dictionary (the `fr_list` file for
  the language) with an "unstressed" attribute `$u` or `$u+` (e.g. in English,
  words such as "the", "is", "had", "my", "she", "of", "in", "some"), or should
  be preceded by a short pause (such as "and", "but", "which"), or have other
  attributes, in order to make the speech flow better.

* Improve the rhythm of the speech by adjusting the relative lengths of vowels
  in different contexts, e.g. stressed/unstressed syllable, or depending on the
  following phonemes. This is important for making the speech sound good for the
  language.

* Make new intonation "tunes" for statements or questions (see
  [Intonation](intonation.md)).

For most of the eSpeak languages, I do not speak or understand the language, and I
do not know how it should sound. I can only make improvements as a result of
feedback from speakers of that language. If you want to help to improve a
language, listen carefully and try to identify individual errors, either in
the spelling-to-phoneme translation, the position of stressed syllables within
words, or the sound of phonemes, or problems with rhythm and vowel lengths.