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This is the wiki page of ScaleMT, a scalable architecture to provide translation web services based on Apertium and other machine translation engines.



Machine translation web service usage is limited to a certain amount of requests per IP. If you want to overcome, please register and get an API key. This way we can track where our traffic come from. Registered users enjoy a more generous traffic limit.

To register, please visit:

Once the registration process is finished, you will receive an API key that must be included in all the requests you perform.


This API is very similar to Google AJAX Language API to make as easy as possible switching to Apertium JSON API. For more information about Google AJAX Language API, see .

There are two resources:


The first one translates pieces of plain text or html code, and the second one lists the available language pairs.

Both resources admit GET and POST http methods. The value of arguments must be properly escaped (e.g., via the functional equivalent of Javascript's encodeURIComponent() method).

Common arguments and response format

These arguments are all optional and common to both resources:

  • key : User's personal API key. Requests from registered users have higher priority.
  • callback : Alters the response format, adding a call to a Javascript function. See description below.
  • context : If callback parameter is supplied too, adds additional arguments to the function call. See description below.

If nor callback neither context arguments are supplied, this is the JSON object returned by both resources:

{ "responseData" : JSON Object with the requested data , "responseStatus" : Response numeric code , "responseDetails" : Error description }

If callback argument is supplied, a call to a function named by the callback value is returned. For instance, if callback argument's value is foo, this is the JavaScript code returned:

foo({ "responseData" : JSON Object with the requested data , "responseStatus" : Response numeric code , "responseDetails" : Error description })

If both callback and context arguments are supplied, the returned function call has more arguments. If callback's value is foo and context's value is 'bar:

foo('bar',JSON Object with the requested data , Response numeric code , Error description )

listPairs resource

This resource only accepts the common arguments.

The response data returned is an array of language pairs, following this format:

[{"sourceLanguage": source language code ,"targetLanguage": target language code }, ... ]

responseStatus is always 200, that means the request was processed OK, and responseDetails has a null value.

So if we call this resource with no arguments:

curl 'http://ApertiumServerInstallationHost/ApertiumServerRouter/resources/listPairs'

we get, for example:


translate resource

This resource accepts the common arguments mentioned above, plus the following specific arguments:

  • q : Source text or HTML code to be translated. Compulsory argument.
  • langpair : Source language code and target language code, separated by '|' character, which is escaped as '%7C'. Compulsory argument.
  • format : Source format. txt for plain text and html for HTML code. This argument is optional. If this argument is missing it is assumed that source is plain text.
  • markUnknown : yes for placing an asterisk next to each unknown word, no for not placing it. This argument is optional. If this argument is missing, an asterisk is placed next to each unknown word.

The response data is JSON object following this format:

{ "translatedText" : translated text }

Many different response status codes can be returned. This is the list with all the codes and their meaning:

  • 200 : Text has been translated successfully, responseDetails field is null.
  • 400 : Bad parameters. A compulsory argument is missing, or there is an argument with wrong format. A more accurate description can be found in responseDetails field.
  • 451 : Not supported pair. The translation engine can't translate with the requested language pair.
  • 452 : Not supported format. The translation engine doesn't recognize the requested format.
  • 500 : Unexpected error. An unexpected error happened. Depending on the error, a more accurate description can be found in responseDetails field.
  • 552 : The traffic limit for your IP or your user has been reached.

Here is a simple example. Requesting a translation with:

curl ''

the result is:

foo({"responseData":{"translatedText":"hola Mundo"},"responseDetails":null,"responseStatus":200})

And if we add the context parameter:

curl ''

we get

foo('a',{"translatedText":"hola Mundo"},200,null)

Batch interface

More than one translation can be performed in the same request if we use more than one q argument or more than one langpair. If there is only one q argument and more than one langpair arguments, the same input string is translated with different language pairs. If there is only one langpair argument and more than one q arguments, the different input strings are translated with the same language pair. And if both arguments are supplied more than one time, and they are repeated exactly the same times, the first q is translated with the first langpair, the second q with the second langpair, etc.

The returned JSON changes a bit when using the batch interface. Now the field responseData contains an array of JSON objects, each one with the usual fields: responseData, responseStatus and responseDetails. Note that we have particular values of responseStatus and responseDetails for each translation, but global values too. If all the translation are OK, these values match, but if there is an error in any translation, global values of these fields take the value of the erroneous translation. If there is more than one erroneous translation, global fields take the value of one the the erroneus translations.

These examples show the described behaviour:

curl  ''
{"responseData":[{"responseData":{"translatedText":"hola Mundo"},"responseDetails":null,"responseStatus":200},

curl  ''
foo({"responseData":[{"responseData":{"translatedText":"hola Mundo"},"responseDetails":null,"responseStatus":200},
{"responseData":{"translatedText":"Món d'hola"},"responseDetails":null,"responseStatus":200}],"responseDetails":null,"responseStatus":200})

curl  ''
foo('bar',[{"responseData":{"translatedText":"hola Mundo"},"responseDetails":null,"responseStatus":200},

Javascript library

If you plan to use the JSON AJAX API from a Javascript client (that's the use the API is intended for), we have a Javascript library that will make that task easier. It is very similar to the Google AJAX Language API one:

To use it, firstly include the library code with:

<script type="text/javascript" src=""></script>

It will import an object called apertium. These are the operations supported by this object:

Method Return type Description
apertium.translate(content,sourceLang,targetLang,callback) None Translates the given content. It is an asynchronous function: instead of directly returning the translation, the callback function is called when the translation is available.
  • content: Can be a simple string, which means that the source is treated as plain text, or an object with two fields:
    • type: the format of the text to be translated. Its values are defined in the object apertium.ContentType. Currently only plan text and HTML are supported.
    • text: simple string containing the txt or html code to be translated.
  • sourceLang: Source language code, e.g. "es", "en", ...
  • targetLang: Target language code, e.g. "es", "en", ...
  • callback: Function to be called when the translation is available. It receive one argument: the translation result. It is an object with the following fields:
    • error. Optional field, only present if there has been any problem with the translation. It has two fields:
      • code: Error code. The valued described previously.
      • message: Description of the error in English.
apertium.isTranslablePair(sourceLang,targetLang) Boolean Returns true if the translation engine can translate the given language pair. Returns false otherwise. Arguments:
  • sourceLang: Source language code, e.g. "es", "en", ...
  • targetLang: Target language code, e.g. "es", "en", ...