Does the French sentence mean that it is rare for people to invest (Investment is rare), or that a particular investment is rare, or scarce, or uncommon (The investment is rare (scarce, uncommon)?
I have the same question.
'uncommon' is probably better than rare.
Or possibly "scarce". If the point of the sentence is that there is a dearth of capital available for investment, then scarce would be the better choice.
Why doesn't it accept 'the investment is strange' as in an observation upon an investment?