"The Polish and Czech names were rarely used before 1945 since the mountain range was almost entirely inhabited by Germans?"
Source or is this another OR ? And please no interwar era German history books that claim Poles never lived in Germanised territories. It's really also non-scholary to talk about Germans since it was rather XIX century creation.
And the name of course should be established one. Fortunetely Czech locations do not fall into enforced Gdańsk vote(which ignored several issues and votes against) so there will be no problem with using Czech names as this is largely the area of Czech history.