That English natives have so much trouble distinguishing effect from affect keeps surprising me.
As for Dutch, the dt-issue is presented as if it is this hugely complicated set of rules. While in reality it is dead simple. Third person in the present time is ALWAYS conjugated as stem+t for regular verbs, except in ONE case: when the stem already ends in t. Dt isn't special, it's just the rule applied to all stems.
I think the main issue with that one is that they've become homophones in a lot of regional accents, a secondary part of it is that they are semi-related concepts, and the third part of it is that there are also technically noun and verb versions of each.
X affects Y, X has an effect on Y.
The affected happiness effect effected a positive affect.
My school taught this whole convoluted system that was meant to help students with multiple tenses, but I just learned to apply the "ik loop" mnemonic which is so effortless (to native speakers at least.)
Sometimes I have to think once or twice about soft ketchup/'t Kofschip for the past participle, but that's about it.
But again, there is no special exception for dt. Again it's the regular rule applied: second person conjugation in questions is just the stem for regular verbs.
I think the main errors happen with "voltooide deelwoorden" (past participle). Then you need mnemonic devices like "'t kofschip" to know whether it's t or d (or determine it using what you would say in the past time of the verb). It doesn't help that e.g., "gebeurt" and "gebeurd" both are correct depending on the tense used.
Also the fact that the t drops when the verb is inversed in the 2nd person singular present tense, and not e.g., past tense ("Je wordt" but "Word je") is a weird rule.
It's not thát complicated and if you pay attention, you should be able to get it all right. That's why I think such mistakes are more a sign of carelessness and not of stupidity.