Learn Turkish: Ormanda yaklaşık on on beş çeşit yenilebilir mantar yetişiyor. - Approximately ten or fifteen varieties of edible mushrooms grow in the forest.

In Turkish, placing two consecutive or close numbers right next to each other creates an approximation. So on on beş literally means 'ten fifteen', but it is naturally understood as 'ten or fifteen'. You do not need to use veya or ya da (or) between them.

The sentence uses both yaklaşık (approximately) and on on beş (ten or fifteen). Isn't that saying 'approximately' twice?

Yes, it is technically a bit redundant, but it is extremely common and natural in Turkish! Using yaklaşık alongside a number pair emphasizes that it is just a rough estimate. You could drop yaklaşık and the sentence would still mean practically the same thing.

Why are çeşit and mantar singular when there are ten to fifteen of them?

As a quick refresher: in Turkish, nouns that follow a number or quantity must remain in their singular form. Because we established the quantity with on on beş, both the classifier çeşit (variety) and the main noun mantar (mushroom) stay singular. Adding the plural suffix -lar to either of them here would be grammatically incorrect.

How do we break down the word yenilebilir (edible)?