Learn Turkish: Bir mal ne kadar otantikse, o kadar pahalı olur. - The more authentic an item is, the more expensive it becomes.

In Turkish, proportional comparisons like 'the more... the more...' are built using ne kadar (however much) in the first clause and o kadar (that much) in the second. The first clause must also include a conditional ending (like -se in this sentence). Literally, it translates to: 'However much an item is authentic, that much expensive it becomes.'

Why is the conditional suffix -se attached directly to the adjective in otantikse?

In this ne kadar ... o kadar structure, the first clause requires a conditional verb. Because there is no action verb here—we are just describing the item's state of being authentic—we attach the conditional suffix -se directly to the adjective otantik. It acts as a "to be" verb, essentially meaning 'if it is authentic.'

Why use olur at the end instead of just saying o kadar pahalıdır?

You could actually use pahalıdır to state a factual description ('it is that expensive'). However, using olur (the aorist or broad-time tense of olmak, meaning 'to become' or 'to be') highlights a natural outcome or a general rule. It gives the nuance that the item 'becomes' expensive or 'tends to be' expensive as a direct result of its authenticity.

I've heard mal used as slang. Is that what's happening here?

No, here it is used in its standard, formal sense. Mal generally means 'goods,' 'property,' 'merchandise,' or 'item.' While it is frequently used as a mild insult in street slang (meaning 'idiot' or 'stupid'), in a commercial or descriptive context like this sentence, it simply refers to a product.