Translation:In a month the decision will definitely have been taken.
I live in Australia, read a lot of books (written by authors from right across the English-speaking world) and have NEVER heard ANYONE say I am going to "take" a decision. We "make" decisons, not "take". I know this is a free program (so shouldn't complain) but I'm starting to lose faith in the authors' understanding of English. This unit is difficult enough without incorrect translations making it even harder to progress.
In is used when the action is complete. Tra when the action is ongoing. We will see him in three weeks....ongoing....Lo vedremo tra tre settimane. It was finished in three weeks...action complete....Era finito in tre settimane. You can also use DA to mean In...when it is really substituting for Per ...meaning For or Since. I haven't been drunk in (for) three weeks.....Non sono ubriaco da tre settimane.
English is a language that evolves, and there aren't any stable grammatical rules. It's all about how it's used. Here's some evidence: https://www.quickanddirtytips.com/education/grammar/take-decision-make-decision
Sorry, you're original comment seemed stronger. 6% of a large number is still large, but in any case, I don't strongly disagree and don't feel a need to continue arguing the point. I'll merely end with an observation and an open question:
It may be that the compiler is one of the minority who regularly "take" decisions. In a course such as this should you insist editors be expert at being rigorously mainstream with respect to usage or allow them to use English as they would naturally?