Download windows 10 bulgarian language pack. If you have an msdn subscription, you can download full microsoft language pack iso image directly from there if you don't have msdn, you can find this file online after a bit of searching if you need english (united states) language pack for windows 10 rtm 64bit (for example to install rsat), you can download it from here.
download windows 10 bulgarian language pack
For more information, see language packs the version of the language, lip, or feature on demand must match the version number for example, you can neither add a windows 10 version 1809 lip to windows 10 version 1803 image, nor add a windows server 2019 language pack to windows server 2016.