Learn Turkish: Yurt dışı pazarında sorun vardı, nitekim ihracatta düşüş oldu. - There was a problem in the market abroad, indeed a decline in exports happened.

Nitekim is used to introduce a real-world result that proves or logically follows the previous statement. It translates to "as a matter of fact," "indeed," or "just as expected." You couldn't use yani (in other words) here because yani just clarifies or rephrases a point, whereas nitekim confirms that the problem in the market actually caused a tangible, expected result.

Why is it yurt dışı pazarında with the extra -ı instead of just yurt dışı pazarda?

This is an indefinite noun compound. The phrase yurt dışı (abroad) acts as a noun concept modifying pazar (market). To link two nouns like this in Turkish, you must add the compound marker -ı to the second noun, making yurt dışı pazarı (overseas market). Finally, you add the buffer -n- and the locative -da to mean "in the overseas market."

Why say ihracatta düşüş (decline in exports) using the locative case instead of ihracatın düşüşü (the decline of exports)?

Both are grammatically correct, but using the locative case (-de/-da) with verbal nouns like düşüş (decline) or artış (increase) is the most standard, natural way to express a change in a specific area or sector. It treats the export sector as the location where the decline occurred.