fix: Support for plural translation forms in translated python

[suricactus]

If there is Python code doing:

Object.tr("%n apple(s)", None, 2)

And I run:

$ qgis-plugin-ci push-translation $TX_TOKEN

I get an exception:

transifex.api.exceptions.UploadException: English pluralized strings should contain 2 plurals. Instead, on string '<translation><numerusform/></translation>' we found 1

The produced output by pylupdate5 in the .ts file is:

<message numerus="yes">
  <source>%n apple(s)</source>
  <translation type="unfinished">
    <numerusform></numerusform>
  </translation>
</message>

We assume that the source language is English.

The problem is that English has 2 plural forms and they must be specified as part of the .ts file as two separate tags:

<message numerus="yes">
  <source>%n apple(s)</source>
  <translation type="unfinished">
    <numerusform></numerusform>
    <numerusform></numerusform>
  </translation>
</message>

While the suggested solution is far from beautiful and optimal, the other explored options did not work better:

1. replace pylupdate5 with lupdate - according to the docs (https://doc.qt.io/qt-6/linguist-lupdate.html), lupdate should parse Python without an issue, but this is not the case, many errors due to failed Python parsing happened:

tr() cannot be called without context
Unterminated C++ string

2. parsing the XML and adding the new tag looks like an overkill, so I stick with a simple search and replace. 3) removing the <numerusform></numerusform> from the .ts file caused:

transifex.api.exceptions.UploadException: English pluralized strings should contain 2 plurals. Instead, on string '<translation><numerusform/></translation>' we found 0

4. seems that lupdate has a nice set of parameters that can help, but are not available in pylupdate5 even after looking at it's internals:

       -source-language <language>[_<region>]
              Specify/override the language of the source strings. Defaults to POSIX if not specified and the file does not name it yet.

       -target-language <language>[_<region>]
              Specify/override the language of the translation.  The target language is guessed from the file name if this option is not specified and the file contents name no language yet.

See it up and running here: https://github.com/opengisch/qfieldsync/actions/runs/16583706724/job/46904935929

[3nids]

have you checked with pylupdate6?

The fix doesn't seem sufficient to me in case this is fixed upstream. If there are 2 tags, we'll get 4, correct?

[3nids]

@suricactus could you update the PR to actually check if the file is incorrect before making the changes?

[suricactus]

I think it will always be incorrect in my understanding how pylupdate5 works. But yes, I can try to do that.

However, I don't see an easy way to achieve this without parsing the XML properly, so I can come back to this later this year.