Fatal error: Uncaught TypeError: WP_Translation_Controller::set_locale(): Argument #1 ($locale) must be of type string, null given, called in /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/l10n.php on line 799 and defined in /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/l10n/class-wp-translation-controller.php:87 Stack trace: #0 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/l10n.php(799): WP_Translation_Controller->set_locale() #1 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-content/plugins/polylang/include/olt-manager.php(106): load_textdomain() #2 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/class-wp-hook.php(326): PLL_OLT_Manager->load_textdomains() #3 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters() #4 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/plugin.php(517): WP_Hook->do_action() #5 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-content/plugins/polylang/frontend/choose-lang.php(112): do_action() #6 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-content/plugins/polylang/frontend/choose-lang-content.php(151): PLL_Choose_Lang->set_language() #7 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/class-wp-hook.php(324): PLL_Choose_Lang_Content->wp() #8 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters() #9 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/plugin.php(565): WP_Hook->do_action() #10 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/class-wp.php(830): do_action_ref_array() #11 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/functions.php(1336): WP->main() #12 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-blog-header.php(16): wp() #13 /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/index.php(17): require('/homepages/10/d...') #14 {main} thrown in /homepages/10/d19502989/htdocs/clickandbuilds/OberschlesischesLandesmuseum/wp-includes/l10n/class-wp-translation-controller.php on line 87