The word banana and variants thereof appear in a number of languages. The origin appears to be the word banaana in Wolof, if Wikipedia is to be trusted. This word is straightforward to adopt into Latin: banana fits perfectly into the first declension.
What is less obvious for me is what to do with vowel lengths. Should it be bānāna, bānăna, bănāna, or bănăna? All four pronunciations are clearly distinct and the stress has two possible places, so it makes a difference.
The third option bănāna seems to best match the stress in many other languages with a similar word, but the connection between Latin vowel length and stress in other languages is not always that straightforward. Stress considerations only effect the second a, not the first one. Somehow a short first a sounds more natural to me, but I cannot articulate why. There are cases where Latin vowel length contradicts my instinct (I would expect plŭs and mīnus as a Finn), so I cannot fully trust it.
What vowel lengths would you pick and why? While I am also interested in the length of a banana specifically, I would like to understand the processes available for deciding these lengths. This question specifically concerns relatively modern borrowings from other languages to Latin, like banana. There can be room for arbitrary choices of course, but I do assume that there often are reasons to prefer some lengths over others.
I should stress that this question is about the process of choosing vowel lengths in borrowed words. Alternative translation suggestions for the fruit therefore miss the point, but they are interesting nevertheless. It is therefore irrelevant, but I would actually prefer the word banana with some lengths, as it most clearly and unambiguously communicates the correct ideas to most modern speakers; the alternatives suggested have sound reasoning behind them, but I find them worse for communication.