Document how to escape a percent symbol in ugettext

[Paolo Dente]

While {% trans %} and {% blocktrans %} correctly escape '%' with '%%' in templates, using ugettext or ugettext_lazy does not; this results in errors with compilemessages.

Example:

price_adjust = models.DecimalField(max_digits=5, decimal_places=2, default=1, choices=(('0.90', _('10% discount'), ))

will generate:

#, python-format
msgid "10% discount"
msgstr ""

When this is translated to German escaping the %, like:

#, python-format
msgid "10% discount"
msgstr "10%% Rabatt"

This results in an error message:

Execution of msgfmt failed: /vagrant/src/locale_files/en/LC_MESSAGES/django.po:xxx: number of format specifications in 'msgid' and 'msgstr' does not match

On the other hand, when it's not escaped, the error becomes:

Execution of msgfmt failed: /vagrant/src/locale_files/en/LC_MESSAGES/django.po:xxx: 'msgstr' is not a valid Python format string, unlike 'msgid'. Reason: In the directive number 1, the character 'R' is not a valid conversion specifier.

Also, while trying to find a solution for this, I've found this suggestion: https://code.djangoproject.com/ticket/24257#comment:2 - which doesn't work for me at all. The only way I found is to use %(percent)s in the string, which is awkward and difficult to read by the actual translators.

[Tim Graham]

Not sure about the correct resolution. All I could find was ​a workaround on Stackoverflow.

[Claude Paroz]

This is not Django specific and this is a documentation issue. There are two solutions that I know of:

• Escape the literal % by doubling it in the string yourself.
• Add a comment on the line before the translatable string containing xgettext:no-python-format.

[Henry Dang]

​PR

[Claude Paroz]

The explanation in the patch is not correct. The fix must happen in the original file, not in the .po file.

[Henry Dang]

Ah, you're right. I've made the changes.

[Tim Graham <timograham@…>]

In b1a90415:

Fixed #27221 -- Doc'd how to escape a percent symbol in ugettext().

[Tim Graham <timograham@…>]

In 047a62b3:

[1.10.x] Fixed #27221 -- Doc'd how to escape a percent symbol in ugettext().

Backport of b1a9041535db5d03dab7f205669f0ab7a47de854 from master