This is false. "Pale of Settlement" refers to part of the Russian Empire and, while some of what is today Poland was then controlled by the Russian Empire, other parts of Poland were under Prussian or Austrian control (see https://en.wikipedia.org/wiki/Partitions_of_Poland).

There was no pre 20th century Poland! The pale is the same as the Polish Lithuanian commonwealth (mostly), minus Habsburg Galicia and the Prussian part of Poland. The nobility of the polish Lithuanian commonwealth were mostly polish or German speaking (and thus there is very little lithuanian or Belarusian in Yiddish even though a huge number of Jews lived in the Lithuanian part of the commonwealth)