Burmese had a lot of loan or adopted words from English for example car is still car in Burmese. However written in Burmese characters.
Burma was former British colony and English is still has legal and official status in most case.. However spoken English is not as good as Indian people.
Christmas is still Christmas in Burmese and if you say “Merry Christmas” most of Burmese people will understand.
ရွှင်လန်း is merry (shwinlaann) is happy or lively. Then you can say christmas in english 😉