In German, sch and tsch are normal phonemes as far as I know, but they use even one more letter to spell them. I checked the origins of all Dutch words startin

In German, sch and tsch are normal phonemes as far as I know, but they use even one more letter to spell them. I checked the origins of all Dutch words starting with sj- some time ago because some of them look and feel native (and because I'm a nerd), but it turned out that indeed all of them are loan words, even e.g. sjorren which comes from Frisian. It looks like all surrounding languages do have these as phonemes, but Dutch doesn't. (Not sure about Plattdeutsch.)