You’re probably not going to confuse anybody by trying to use two-letter abbreviations for days. But English doesn’t do that.
It may seem really cool to use abbreviations and make it look like a native text. Unfortunately, you’ve got to use the right ones.
- Dutch likes to use two-letter abbreviations (ma-di-wo-do-vr-za-zo).
- English almost invariably prefers three (Mon-Tue-Wed-Thu-Fri-Sat-Sun).
Two letters would admittedly be entirely unambiguous in English too, but for some reason it just isn’t done. Perhap because simply removing “day” from the end leaves you with three letters in several cases.
Prevalence: high. Timetables and opening hours on websites are full of this mistake, for instance – anywhere that the two-letter abbreviations get used in Dutch.
Frequency: very high. Obviously liable to occur many times in a single document or webpage or whatever.
Native: no. The only common occurrence of two letters is in the weekday sequence M-Tu-W-Th-F.