Are there any letters/sounds that natives in your language struggle with and have to intentionally learn?

To be more precise, are there letters that natives of your language struggle to pronounce, or are there letters/sounds that they find hard to differentiate?

For example in Bosnian, many kids struggle with pronouncing the letter r (trilled).

Also many people can't differentiate between the letters č and ć both when writing and in speech, so kids in schools have to learn this and even have these kinds of exercises on exams.