Following the changes made when discussing https://phabricator.kde.org/D4008:

Some changes in the INSTALL file because, as stated in the new https://krusader.org/get-involved/index.html page:

Note: On a multi cpu/core system you might want to speed up the compile process by increasing the number of jobs (e.g. "make -j4").

and because nowadays a particular command using wget can download a krusader.po file.