▁du cal ▁court ▁already ▁used ▁Polish ▁as ▁their ▁first ▁language . ▁The ▁last ▁Grand ▁Duke ▁known ▁to ▁have ▁spoken ▁Lith uan ian ▁was ▁Cas imir ▁IV ▁J agi ell on ▁( 1 4 4 0 - 1 4 9 2 ). ▁In ▁ 1 5 9 5 ▁Mik al oj us ▁D au k š a ▁addressed ▁Lith uan ian ▁nob ility ▁calling ▁for ▁the ▁Lith uan ian ▁language ▁to ▁play ▁a ▁more ▁important ▁role ▁in ▁state ▁life . ▁The ▁usage ▁of ▁Lith uan ian ▁decl ined , ▁and ▁the ▁Polish ▁language ▁became ▁the ▁pre domin ant ▁administrative ▁language ▁in ▁the ▁ 1 6 th ▁century , ▁eventually ▁replacing ▁Ruth en ian ▁as ▁the ▁official ▁language ▁of ▁the ▁Grand ▁Duch y ▁in ▁ 1 6 9 7 . ▁Non eth eless , ▁spoken ▁Lith uan ian ▁was ▁still ▁common ▁in ▁the ▁Grand ▁Duch y ▁courts ▁during ▁the ▁ 1 7 th ▁century . ▁ ▁At ▁first ▁only ▁Lith uan ian ▁magn ate ▁families ▁were ▁affected ▁by ▁Pol on ization , ▁although ▁many ▁of ▁them ▁like ▁the ▁Rad zi wi ł ł s ▁remained ▁loyal ▁to ▁the ▁Grand ▁Duch y ▁of ▁Lith u ania ▁and ▁saf egu arded ▁its ▁so vere ig nt y ▁vis - à - vis ▁the ▁Kingdom ▁of ▁Poland . ▁Grad ually ▁Pol on ization ▁spread ▁to ▁wider ▁population , ▁and ▁for ▁the ▁most ▁part ▁Lith uan ian ▁nob ility ▁became ▁part ▁of ▁both ▁nations ’ ▁sz lach ta . ▁ ▁The ▁middle ▁nob ility ▁adopted ▁the ▁Polish ▁language ▁in