Use the [ddd], [Ddd] or [DDD] day token to get a shortened version of the weekday name for the current date and current language.
the values of the [ddd] token in French showing some months abbreviations using 4 letters
All three tokens give the same result. The only difference is the capitalization.
Note that this token does not necessarily abbreviate the weekday name to 3 letters. It displays whatever translation you have set for the [mmm] tokens in the tokens manager. For each script you can additionally specify that you wish to only have a limited number of letters (see the length of [ddd] option).
So, on Tuesday, October 12th, in English, the result may be :
•[ddd] = tue
•[Ddd] = Tue
•[DDD] = TUE
The reason why we say the result may be, is that the above tokens are mixed source tokens. Q++Studio will decide, based on the current date, which day of the week it is, but it will then look for the translation that you supplied for 'Mon', 'Tue', 'Wed' … in the current language.
Since you specify the translations, you have total freedom. For example you may decide that in Swedish the shortened weekdays are not the first 3 letters (as in English), but the first 4 letters. Similarly you can easily create a descendant language based on English, where the [ddd] tokens are replaced by only the 2 first letters of the weekday name (although in this case it would be simpler to use the length of [ddd] GridOption).