This is the 12073rd most frequent Polish word.
litewskiego
"Litewskiego" means "Lithuanian" (genitive or accusative singular form in Polish).
Here, 'litewskiego' is used as an adjective in the genitive case to describe 'języka' (language), illustrating its function in specifying the type of language.
Czy znasz historię litewskiego języka?
Do you know the history of the Lithuanian language?
In this sentence, 'litewskiego' does not appear directly; instead, the base form 'litewski' is in use as 'po litewsku' (in Lithuanian). It shows the adverbial application of the word.
Mam przyjaciela mówiącego po litewsku, który uczy się polskiego.
I have a friend who speaks Lithuanian, who is learning Polish.
Here, 'litewskiego' describes the kind of dictionary ('słownika') in the genitive case, indicating a possession or relation to the Lithuanian language.