Changes in language file loading
From Joomla! Documentation
Errors reported[edit]
Because of how Joomla previously parsed the language INI files, it was possible for files with invalid syntax to be loaded without any errors raised. With a change in 3.7, these files may no longer load correctly.
Versions affected[edit]
General Information
This pertains only to Joomla! version: 3.7.0 and above
What is the cause[edit]
Since 3.7.0, the language file parser has been updated to use the PHP parse_ini_file function which will raise an error if invalid syntax is detected.
How to fix[edit]
Please fix the language strings to be correct and valid. You can check that by running the file against parse_ini_file e.g. using the command line or a PHP script.