I just read the 2008 census final results and made a table on the French Wikipedia summarizing the numbers of speakers here : https://fr.wikipedia.org/wiki/Langues_au_Cambodge#Langues_maternelles
but I almost see no matching in most cases even if you cite the exact same 2008 census! Would you have an explanation ? Moreover, the census lists 33 languages including 23 minority languages (you count 22), 9 foreign languages (Chinese, French, etc.) and 1 national language (Khmer).