fix test case for _() in templates, improve documentation

[Antti Kaihola]

The _() construct available for templates doesn't work ​as explained in the documentation, and there are no actual unit tests for it either.

Here is a test script to illustrate the problem:

from django.conf import settings
settings.configure(LANGUAGE_CODE='fi')

from django.template import Template, Context

template = Template(
    u'{% load i18n %}'
    u'{% trans "Yes" %} '
    u'{{ true|yesno:_("Yes,No") }} '
    u'{{ false|yesno:_("Yes,No") }}')

context = Context({'true': True, 'false': False})
print template.render(context)

This should print out the Finnish translation of "Yes" twice and "No" once:

Kyllä Kyllä Ei

but only {% trans %} works correctly, and the script in fact prints

Kyllä Yes No

There's [source:django/trunk/tests/regressiontests/templates/tests.py#6996#L739 a test case] which probably is meant to test this, but fails to do so:

'i18n10': ('{{ bool|yesno:_("ja,nein") }}', {'bool': True}, 'ja'),

I assume this is what was intended:

'i18n10': ('{{ bool|yesno:_("Yes,No") }}', {'bool': True, 'LANGUAGE_CODE': 'de'}, 'Ja'),

and it currently fails:

Template test (TEMPLATE_STRING_IF_INVALID='INVALID'): i18n10 -- FAILED. Expected 'Ja', got u'Yes'

[Antti Kaihola]

fix for the test case (same as in bug description)

[Antti Kaihola]

Oops, I misunderstood the documentation when writing the original bug report ("_() broken in templates"). But there actually is still a problem in unit tests and room for improvement in the documentation.

Maybe it should be clarified ​in the documentation for _() in templates that |yesno:_("yes,no") actually looks for the string "yes,no" in the translation files, not for "yes" and "no" separately.

And it would be better to use an actual existing translation string like "yes,no,maybe" instead of "yes,no" in the example.

Also, [source:django/trunk/tests/regressiontests/templates/tests.py#6996#L739 the test case for _() in templates] is invalid:

'i18n10': ('{{ bool|yesno:_("ja,nein") }}', {'bool': True}, 'ja'),

This should be better, and it does pass:

'i18n10': ('{{ bool|yesno:_("yes,no,maybe") }}', {'bool': True, 'LANGUAGE_CODE': 'de'}, 'Ja'),

[Antti Kaihola]

Opened a new ticket for the unit test and documentation improvement suggestions.