The answer is really, "it's up to you," but for myself I like to think that I would remember the place where the plant grows, and be able to return there. Feel free to introduce your own rules. In solo roleplaying I often use a freeform probability system based on a rough estimate of how likely something seems to me. If I'm using just D6, I might say "roll from 1-4 to succeed at finding this plant again today." Or, if it feels like a rarer plant, I might say "Roll from 1-2" etc.
Here's a thought: When you discover a plant, roll a 1d6 to discover the "rarity" of that plant. To find the plant again on a given day, roll equal to or below the rarity. (Or some variation on this idea.)
I think many solo roleplayers like to experiment with rules, and will often mix in mechanics from many different games. I like to design with this "bring your own rules" idea in mind.
Yes, please feel free to translate the game into French. I'd love to see the result, if you do so. :)
Thank you! :)