Hi,
I suggest you refer to this support article, as the article said the language name for Windows Language and Office Language are different:
https://support.microsoft.com/en-au/office/office-displays-in-english-instead-of-chinese-or-serbian-482fcb3d-2cc7-492b-88a8-80d5bfe4d7fd For Office, you can download the Serbian (Latin, Serbia) from this link: https://support.microsoft.com/en-us/office/language-accessory-pack-for-microsoft-365-82ee1236-0f9a-45ee-9c72-05b026ee809f#ID0EBBF=Office_2021 Just checking in to see if the information was helpful. Please let us know if you would like further assistance.
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