Two runs of lupdate are required if -pluralonly is used for the native language

This is more a conceptional problem than a bug.

Qt's i18n documentation suggests to create a plural-only translation of the project's native language, see https://doc.qt.io/qt-5/i18n-source-translation.html#handling-plurals

This requires to run lupdate with the -pluralonly argument for the native language and without that argument for all other languages:

lupdate -pluralonly -ts myproject_en.ts ...
lupdate -ts myproject_de.ts myproject_da.ts myproject_pl.ts ...

That means the project's sources are scanned twice, doubling the time that's needed to update the .ts files.

Possible solution:

• specify plural-only .ts files on the command line with -pluralonly-ts myproject_en.ts
• or somehow post-process an updated .ts file by removing the non-plural messages from there