Complex sentence: In January 2018 the Polish Parliament (the Sejm) adopted an Amendment to the Act on the Institute of National Remembrance--legislation which, among other things, outlawed use of the phrase "Polish death camp".
Split into simpler sentences: In January 2018, the lower house of the Polish parliament (the Sejm) approved a bill, the Amendment to the Act on the Institute of National Remembrance. Among other things, it would outlaw use of the phrase "Polish death camp".