I just read a report that selfie, hashtag and tweet are now going to be included in the dictionary of Malay published by the Malaysian Dewan Bahasa dan Pustaka ('Language and Literature Bureau'). They will be labelled as 'bp', which stands for bahasa percakapan ('colloquial language'), as they are not regarded as bahasa baku ('standard language').
The rationale for including these words is that it is the job of a dictionary to reflect actual usage. On this basis, I wonder when they will include so and then as words of Malay. I regularly hear people using these two words in utterances that are otherwise completely Malay, so it seems it is only a matter of time before they are completely accepted as Malay words.