Analysis of information sources in references of the Wikipedia article "วันแห่งความตาย" in Thai language version.
According to Aguirre, Día de los Muertos ... is a direct translation from the English translation of Día de Muertos. Día de los Muertos is simply an American translation, while folks in Mexico refer to the celebration without the “los”.
Dia de Los Muertos is the direct translation of Day of the Dead, the los is not needed.
...when Mexico begins celebrations for Día de los Muertos (better known in Mexico as Día de Muertos).