1. Check app/Services/HousekeepingService.php and index.php to delete unwanted files from previous version while upgrade and update upgrade.php accordingly.

[0] Fix | Delete

2. PHP REQUIREMENT LINK: https://webtrees.net/install/requirements/

[1] Fix | Delete

3. Download webtrees-x.y.z.zip package from github and not source code as webtrees-x.y.z.zip contains language files.(confirmed vendor)

[2] Fix | Delete

4. Delete entries of SITE_UUID,LATEST_WT_VERSION and LATEST_WT_VERSION_TIMESTAMP from site_setting and log table, created when accessed.

[3] Fix | Delete