i guess i found the solution
go to ubi launcher, then set language as english.
after starting game, you can choose your own language in in-game option
It works, but you need to change the language to English, not the Ubosoft launcher, but in the game's properties.
Normally I always choose the Polish language version. This is how, for example, the Legion is set up. Valhalla doesn't display any subtitles or hear the dialogue path with these settings. After English is set, everything is fine - game sounds are in English and subtitles are in Polish.