Language code in translated .po file header entry improperly changed to 'en'

[jflann]

Summary

Language code in translated .po file header entry improperly changed to 'en'

Steps to reproduce

Translate files via gitlocalize and submit to repository via PR.

Repository URL

example PR with issue

What is the current bug behavior?

The language code in the .po file is changed from 'fr' to 'en'

What is the expected correct behavior?

The language code in the .po file should either not be changed or be changed only if it differs from the code of the language the file represents.