qtranxf_resolveLangCase() called with array

[BabelhalSupport]

Describe the bug
qtranxf_resolveLangCase(): Argument #1 ($lang) must be of type string, array given, called in /.../wp-content/plugins/qtranslate-xt/src/language_detect.php on line 216

To Reproduce
Steps to reproduce the behavior:

1. Install qTranslate-XT plugin
2. Go to URL https://{domain}/?lang[lang]=de

Expected behavior
No PHP error should occur.

Debug info

qTranslate-XT version: 3.15.2

Additional context
I do not known, why anyone would try to load such an URl, but someone did at our website.