This is the user’s true desire. A "Language Pack" is a collection of files—specifically .dat, .fat, or .xml files within the game’s data_win32 folder—that contain the English voice-over lines, English subtitles, and English UI text. Ubisoft does not always include every language with every download to save bandwidth. If you bought the "RU/CIS" version (Russia/Commonwealth of Independent States), you got Russian. If you bought the German version, you got Deutsch. The English pack is the "unlock key" to turn your foreign copy into a native English experience.
Malicious actors often rename malware payloads to unusual extensions to bypass naive file filters or to confuse users. You might find this .epub file on torrent sites or "free game" forums. Far Cry 3 English Language Pack.epub
Ubisoft Connect
If the game still shows another language after switching: This is the user’s true desire