Date format in RSS feeds follows system language which is not interpreted correctly when exported

Summary

When changing the system language in JIRA to French and exporting RSS feeds, the <pubDate> parameter changes to the french language format. This is not interpreted well when exporting to emails such as outlook where the date is being rendered differently until previewed.

Steps to Reproduce

1. Go to profile > preferences > language, and change the language to French.
2. Go to search for issues and Export RSS.
3. Look for the <pubDate> parameter.

Expected Results

1. The <pubDate> parameter should stay in English.

Actual Results

1. The <pubDate> parameter changes to French.

Workaround

Upgrade the JIRA instance to version 7.0 and higher where this issue has been fixed.