Port extractxml to Python 3 with minor typo fixes

Summary: Minor porting with some typos fixed, in case it will be needed some day

Test Plan: Tested with https://phabricator.kde.org/D25405 and seems to work as expected.

Reviewers: Localization, adrianchavesfernandez

Reviewed By: adrianchavesfernandez

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D25532