Upload to Crowdin with non-ASCII characters in source translation fails

[sebastian]

How to reproduce

Run ./build.py -t chrome translate <API_key> from adblockpluschrome.

Observed behaviour

No translations are submitted to Crowdin. The following error is logged to stderr:

Traceback (most recent call last):
  File "./build.py", line 18, in <module>
    buildtools.build.processArgs(BASE_DIR, sys.argv)
  File "/home/sebastian/src/adblockpluschrome/buildtools/build.py", line 607, in processArgs
    commands[command](baseDir, scriptName, opts, args, type)
  File "/home/sebastian/src/adblockpluschrome/buildtools/build.py", line 55, in __call__
    return self._handler(baseDir, scriptName, opts, args, type)
  File "/home/sebastian/src/adblockpluschrome/buildtools/build.py", line 328, in updateTranslationMaster
    basename, key)
  File "/home/sebastian/src/adblockpluschrome/buildtools/localeTools.py", line 404, in updateTranslationMaster
    data, headers = crowdin_prepare_upload(update)
  File "/home/sebastian/src/adblockpluschrome/buildtools/localeTools.py", line 356, in crowdin_prepare_upload
    ).format(boundary=boundary, name=name, data=data, mimetype=mimetype)
UnicodeEncodeError: 'ascii' codec can't encode character u'\u2026' in position 4772: ordinal not in range(128)

This seems to be a regression introduced with #5777. This bug is only being triggered when the source translation contains any non-ASCII characters.

Expected behaviour

The source translations on Crowdin should be updated with the content from _locales/en_US. No error should occur.

[abpbot]

A commit referencing this issue has landed:
​Issue 5815 - Fixed Crowdin upload with non-ASCII characters