Microsoft Office: 2016 -vl- - Bulgarian Language Pack X64

to set Bulgarian as default for new users:

The for Volume Licensing (VL) is an essential add-on for organizations using the 64-bit version of Office 2016 in a multilingual environment. It enables users to switch the Office user interface, help documentation, and proofing tools (such as spell checkers) to Bulgarian. Key Features Microsoft Office 2016 -VL- - Bulgarian Language Pack X64

Uses Windows Installer (MSI) technology common in enterprise environments. to set Bulgarian as default for new users: