The strong synchronization work added warnings to export.php. Currently repong needs to call export.php twice per group to handle special cases such as message documentation and British English. This causes those warnings to appear twice in the output of automatic exports.
By extending export.php with new command line parameters, we can avoid calling it twice. This avoid showing warnings twice, and potentially let us simplify code in repong. This should not have a major impact in performance (in either direction).
This is a follow-up to T182433: Implement a stronger synchronization in RepoNG and Translate
The output log from automatic translation exports is now shorter simpler and thus easier to review.