A Python 3 script that inverses the translation direction of a .po file and modifies the linked sources.

invert_po.py

"""
For our PHP website, I needed to reverse the translation direction of the i18n functionality. The source code was all in 
Dutch, but since international people had joined our team it made sense to change it to English in order to make their
work easier. This script was created to ease that process.

Please note that this isn't perfect: it won't correctly escape special characters that are inserted into the code, and 
it also won't replace strings that contain escaped characters. It does make the entire process a lot less tedious, though.

Copyright (c) 2018 Martijn Luinstra
"""

import argparse
import os
import re

from babel.messages.catalog import Catalog
from babel.messages.pofile import read_po, write_po

parser = argparse.ArgumentParser(description='Reverse the translations of a PO-file and modify the respective code.')
parser.add_argument('po_file_in',  type=argparse.FileType('rb'))
parser.add_argument('po_file_out', type=argparse.FileType('wb'))
parser.add_argument('--base-path', type=str, default=os.path.realpath(__file__))
args = parser.parse_args()


def replace_content(message):
    for location in message.locations:
        if not message.id:
            continue

        with open(os.path.join(args.base_path, location[0])) as f:
            content = f.read()

        if message.pluralizable:
            new_content = re.sub(r'__N\((\s*)(\'|"){0}(\'|"),(\s*)(\'|"){1}(\'|")'.format(re.escape(message.id[0]), re.escape(message.id[1])),
                                 r'__N(\g<1>\g<2>{}\g<3>,\g<4>\g<5>{}\g<6>'.format(message.string[0].replace('\\', '\\\\'), message.string[1].replace('\\', '\\\\')),
                                 content, flags=re.MULTILINE)
        else:
            new_content = re.sub(r'__\((\s*)(\'|"){0}(\'|")'.format(re.escape(message.id)),
                                 r'__(\g<1>\g<2>{}\g<3>'.format(message.string.replace('\\', '\\\\')),
                                 content, flags=re.MULTILINE)

        with open(os.path.join(args.base_path, location[0]), 'w') as f:
            f.write(new_content)


def run():
    catalog = read_po(args.po_file_in)
    for message in catalog:
        replace_content(message)
        new_catalog.add(
            message.string,
            message.id,
            message.locations,
            message.flags,
            message.auto_comments,
            message.user_comments,
            message.previous_id,
            message.lineno,
            message.context
        )
    write_po(args.po_file_out, new_catalog)
    print ('Done! :)')


if __name__ == "__main__":
    run()