Allow definition of custom locales

For a current project I would like to define a custom locale (let’s call it an ‘in-house-dialect’). It would be nice to be able to add it, preferably by inheriting the properties from an already available language.

Rough sketch:

pybabel init -i messages.pot -d translations --locale="dialect" --base="en"

[kolypto]

@lt3Dev sure, by all means, please do! Let’s say the code is under the MIT license or beerware license 😄

[kolypto]

In the meanwhile, this snippet can be used to hack locale data:

def hack_babel_core_to_support_custom_locales(custom_locales: dict):
    """ Hack Babel core to make it support custom locale names

    Args:
        custom_locales: Mapping from { custom name => ordinary name }
    """
    from babel.core import get_global

    # In order for Babel to know "en_CUSTOM", we have to hack its database and put our custom 
    # locale names there.
    # This database is pickle-loaded from a .dat file and cached, so we only have to do it once.
    db = get_global('likely_subtags')
    for custom_name in custom_locales:
        db[custom_name] = custom_name

    # Also, monkey-patch the exists() and load() functions that load locale data from 'babel/locale-data'
    import babel.localedata

    # Originals
    o_exists, o_load = babel.localedata.exists, babel.localedata.load

    # Make sure we do not patch twice
    if o_exists.__module__ != __name__:
        # Definitions
        def exists(name):
            # Convert custom names to normalized names
            name = custom_locales.get(name, name)
            return o_exists(name)

        def load(name, merge_inherited=True):
            # Convert custom names to normalized names
            name = custom_locales.get(name, name)
            return o_load(name, merge_inherited)

        # Patch
        babel.localedata.exists = exists
        babel.localedata.load = load

        # See that they actually exist
        for normalized_name in custom_locales.values():
            assert o_exists(normalized_name)

Usage:

hack_babel_core_to_support_custom_locales({
    'en_CUSTOM': 'en',  # custom => original
})