in brief, 察爾汗 is derived from mongolian.
the long explanation:
about 1763, there was a large-scale standardisation of names from mongolian, tibetan and various languages used by muslim into han chinese and manchurian. the result was the 24-volume book "欽定西域同文志" (~ made by imperial order 欽定, western region 西域, same language 同文, record 志).
the internet ...