Error in wordpress and crashes site

hello, we would like to buy polylang but it crashes our site, please help in regards to that, the error displayed is

Notice register_uninstall_hook was called incorrectly. Only a static class method or function can be used in an uninstall hook. Please see Debugging in WordPress for more information. (This message was added in version 3.1.0.) 1
–
MW_Polylang_Theme_Strings->__construct()
wp-content/plugins/polylang-theme-strings/mw-polylang-theme-strings.php:13
MW_Polylang_Theme_Strings->Init()
wp-content/plugins/polylang-theme-strings/mw-polylang-theme-strings.php:28
MW_Polylang_Theme_Strings->Plugin_Install_Hooks_Init()
wp-content/plugins/polylang-theme-strings/mw-polylang-theme-strings.php:69
register_uninstall_hook()
wp-content/plugins/polylang-theme-strings/mw-polylang-theme-strings.php:90
wp-includes/functions.php:4161

and the debug log because of polylang shows this:

[05-Nov-2018 07:03:01 UTC] PHP Notice: register_uninstall_hook was called incorrectly. Only a static class method or function can be used in an uninstall hook. Please see Debugging in WordPress for more information. (This message was added in version 3.1.0.) in C:\inetpub\wwwroot\wp-includes\functions.php on line 4161
[05-Nov-2018 07:03:01 UTC] PHP Notice: register_uninstall_hook was called incorrectly. Only a static class method or function can be used in an uninstall hook. Please see Debugging in WordPress for more information. (This message was added in version 3.1.0.) in C:\inetpub\wwwroot\wp-includes\functions.php on line 4161
[05-Nov-2018 07:03:03 UTC] PHP Notice: register_uninstall_hook was called incorrectly. Only a static class method or function can be used in an uninstall hook. Please see Debugging in WordPress for more information. (This message was added in version 3.1.0.) in C:\inetpub\wwwroot\wp-includes\functions.php on line 4161
[05-Nov-2018 07:03:03 UTC] PHP Notice: register_uninstall_hook was called incorrectly. Only a static class method or function can be used in an uninstall hook. Please see Debugging in WordPress for more information. (This message was added in version 3.1.0.) in C:\inetpub\wwwroot\wp-includes\functions.php on line 4161

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