Steps to reproduce the issue

Call from an extension to JHelperContent::getCurrentLanguage()

Expected result

Should return the language code.

Actual result

Undefined variable: langCode in getCurrentLanguage

There is a test on langCode but that variable is not set if the site is not multi-lingual.

System information (as much as possible)

since Joomla 3.7 apparently.

Additional comments

The function should be able to be called without assuming the site is multi-lingual.