How can we know the nuances of the language, especially if the hint for "exterior" includes the word outside? If Brazilians automatically think overseas then don't include outside in the hints
He has taken a decision to go abroad OR He took a decision to go abroad - Why are these both wrong?
Would "ele fez.." also work?
although people understand you, it does not sound natural.
Actually, no. It works for English, but in Portuguese you have to use the verb "tomar".
Could exterior in this context also mean "outside" or shoud I just stick to using "fora" for that?
When you say exterior, we autlmatically think "abroad", not "outside".
In US English we don't "take" a decision, we make or reach one. I'm not sure about the UK. Better to say,"He decided"