Thank you for your reply @sergerdn. From what I know the language components of the header differ from Browser to browser slightly, it's also what BAS states in the help text of "Set browser location by IP" action. There they recommend to use fingerprint instead for increased realism. So the information there is clearly wrong, and misleading. I think one year ago or so it has been changed automatically, as it still changes timezone. Which also explains how the misleading information came there in the first place. Sad that seem not to maintain this functionality, it's pretty easyly detectable thing if all the frech devices that start doing actions have an english browser. So I will be stuck to one Browser type nd set it manually with Set Header or have to read the fingerprint and parse like you suggested.
Help text of "Set browser location by IP" Action
*"Change browser language according to country of ip. This setting will change 'Accept-Language' header as well as navigator.language and navigator.languages javascript properties. By default language value will be equal to language and country code separated with dash, for example 'de-DE' for Germany. This value is valid, but most browsers uses more complicated strings. If you want to make BAS look like real browser, use FingerprintSwitcher service, it will set language to more natural value, for example for iPhone from Germany it will equal 'de, en;q=0.8, ;q=0.01'. You can also set this value explicitly by using 'Set Header' action"