How to handle Open edX XBlocks localization

Posted by surF on December 6, 2017

Open edX is the platform which powers MOOC websites like, Stanford’s Lagunita and many other MOOC providers worldwide. Since it has been released with a FOSS license, its adoption has wildly increased and right now millions of users worldwide are using such a platform for their online courses. As such, the possibility to translate the interface should be a top priority but, unfortunately, not all the components have such a functionality out of the box. In fact, the platform’s external modules, also called XBlocks, are difficult to translate and this article is meant to depict all the possible ways to approach such a task.

Localization is handled pretty well in the edx-platform: there are dedicated tools to handle all the translation processes and teams on Transifex which help translating the interfaces and the contents [you may join them here].

However, for what concerns the external modules which can be integrated in the platform, called XBlocks, there are still issues to be faced and there are ongoing efforts by the edX engineers in order to solve them. The existing integrated translation solution is not working at the moment of writing (if you are lucky you may see the bug here).

Some XBlocks are correctly translated like, e.g., ORA2 or edX Proctoring. However, they are just isolated cases and, unfortunately, not all the XBlocks developers follow the translations guidelines.

In order to understand the nature of this problem it is necessary to understand what is the nature of an XBlock inside the Open edX structure. At the moment of writing, XBlocks are not Django Apps but they can be seen as standalone modules. In fact, XBlocks should be coded in an independent way with respect to the edx-platform and it could also be possible to run them as standalone. Originally called XModules, XBlocks should use standard Python and Mako template engine exactly for the up-cited purpose. Furthermore, for development purposes, it is possible to use a standalone software development kit which does not require a running instance of Open edX installed (see here) and makes it handy to develop new functionalities. This means that the developers have to follow some strict guidelines regarding the implementation of such blocks like, e.g., the templating engine used, and this is causing some issues with the interoperability with the existing localization engine.

For the sake of this quick guide, let’s first of all analyze the way Django handles translations. First of all, all the message files containing the translations in a given language, characterized by the .po extensions, are compiled into the machine readable .mo binary files. This usually in Django is done by using the

django-admin makemessages -a

but in Open edX there are several other ways to do this, i.e. using the i18n suite mentioned before. Afterwards, these message files have to be seen by Django in order to be correctly applied. The order of the search is the following:

  1. the directories listed in LOCALE_PATHS have the highest precedence, with the ones appearing first having higher precedence than the ones appearing later.
  2. Then, it looks for and uses if it exists a locale directory in each of the installed apps listed in INSTALLED_APPS. The ones appearing first have higher precedence than the ones appearing later.
  3. Finally, the Django-provided base translation in django/conf/locale is used as a fallback.

So, analyzing the list we can see how number 2. is not our case since declaring an XBlock as a Django App is not a best practice. I have tried this and it works without problems but many developers advised me that it’s not an encouraged practice, even if a UI Architect at edX told me that it’s not a problem (check out the thread here). However, it seems that in the futures XBlocks will be proper Django apps and this can be seen in this OEP here.

Also, point number 3. is not so straightforward since it would mean that for each new XBlock installed we ought to move the translation files to that specific django folder, to create a new .po file and finally a .mo one. Not very handy.

Solution number 1. might a good pick since, by explicitly telling Django where to look at, it should be able to pick the new translations.

I tried to implement the different solutions and they are all depicted in this commit.

The following piece of code adds solution number 1. to the lms/ file which is invoked during startup.

def enable_locale_discovery():
    Enables Django to see and apply the translations in the XBlocks
    After retrying all the xblocks currently installed, it checks whether a
    `translations` folder exists and adds it to the LOCALE_PATHS list. 
    import inspect, os
    from xblock.core import XBlock

    # Folder name where the XBlocks' translations are located
    locale_folder = 'translations'
    # Retry list of loaded XBlocks
    xblocks_list = XBlock.load_classes()
    for name, class_  in xblocks_list:
        # For each XBlock, get the absolute path of the compiled file 
        xblock_install_path = inspect.getfile(class_)
        # Paths have a recurrent form:
        # `/edx/app/edxapp/<install_path>/<xblock>/<xblock>/xblock.pyc`
        # Strip first '/edx/app/edxapp/' and last 'xblock.pyc' from the path
        stripped_path = xblock_install_path.split('/edx/app/edxapp/',1)[1].rsplit('/',1)[0]
        # Build path using ENV_ROOT
        translated_url = settings.ENV_ROOT / stripped_path / locale_folder
        # Check if the folder exists and if it is not empty
        if(os.path.isdir(translated_url) and os.listdir(translated_url)):
            # Check for unicity and then add to LOCALE_PATHS
            if(translated_url not in settings.LOCALE_PATHS):
                settings.LOCALE_PATHS = ( translated_url , ) + settings.LOCALE_PATHS

So in the way depicted above it is possible to add each XBlock’s translation folder to the LOCALE_PATHS read by Django and the translations are applied consequently.

Another solutions implemented by Felipe Montoya implies the definition and the usage of an extra Django app called django-xblock-i18n. This app basically defines a new service which has to be loaded inside the context of the XBlock and then it can be used. Furthermore, the xblock_i18n tag has to be added at the top of the template tag to be used. For more extended info check the repo I forked which contains some more information about how to use the app in the README file here.

The possibility of merging the .po files together is always possible even if it is highly unrecommended due to all the possible problems that may occur especially during upload - i.e. all the work would be lost after each upgrade. However, what follows is the procedure to accomplish such a task. For each XBlock to be localized, apply the following passages:

  • extract the strings to be localized from all the files like, e.g., .py and .js ones. For python:

    $ find . -name "*.py" | xargs xgettext --language=python --add-comments="Translators:"

    For javascript:

    $ find . -name "*.js" -o  -path  ./public/js/vendor -prune -a -type f | xargs xgettext --language=javascript
    --from-code=utf-8 --add-comments="Translators:"

    Note that each command generates a message.po file, so after running the first time make sure to mv the file to another name.

    NB: there is the possibility of adding --join-existing to the second command but, at the moment of writing, it is not working on my machine. That should help appending the second output to the first message.po file.

    Anyway, Django expects to have a django.{po,mo} file in its locale directory which means that those messages.{po,mo} files have to be renamed.

    For our case, all the strings extracted from python should exist in the django.po file, whilst the ones related to javascript should be inserted inside the djangojs.po file.

    To check if django.po is correct, you can run msgfmt to build a file:

    $ msgfmt django.po -o 

    If everything is correct, the resulting file has to be move to the final directory: translations/<lang_code>/LC_MESSAGES/ Same for the djangojs.{po,mo} files.

  • Now that the .po file is generated, it is necessary to attach it to the platform’s one located in /conf/lang/<lang_code>/django.po. When merging the two files, make sure that there are no conflicting strings (strings which are present in both files). If there are, remove the ones present in the new django.po file and leave the originals intact. Once the merge is finished, it is possible to run the command to generate the new file as before:

    $ msgfmt conf/locale/<lang_code>/LC_MESSAGES/django.po -o translations/<lang_code>/LC_MESSAGES/ 

From now on, Django will read from those files and apply the translations globally. However, as cited above, this is not recommended for obvious reasons.

So, in order to conclude, we have explored the various paths that Django checks to spot the .mo files containing the translations to apply. Three solutions have been proposed, which are more of a workaround than real solutions but they may work while waiting for the official solution. Solution number 1. is what I consider being the best one since it’s not as invasive as the others: solution number 2. adds a Django App to the system whilst 3. is a big mess since it basically implies that all the translation will be merged in a big centralized file which, after an update or a change, will be changed and will lose the mods.

Let me know what you think and if what I wrote may be deemed acceptable.

That’s all folks! :)