Coming from years of studying Korean, @duolingo is a decent practice tool, but I have a few gripes with how it impedes progress and how deals with subject-object-verb languages like Korean.

① It forces you to write perfectly in your native language (English in my case), despite impeding the target language learning process. Your should stay in the target language mode!

This context switch slows the learning process down. How to fix it this

② It should be more flexible with answers and accept awkward word order.
함께 = together, 등산합시다 = let's hike
But "together let's hike" is marked as incorrect by Duo.

Just let me keep the same word order and move on

③ Duo also forces using English particles(?) like "the". These are either implied or non-existant in Korean, so this just wastes time.
✕ at museum let's study (ideal)
✕ let's study at museum (compromise)
✓ let's study at the museum (marked correct but waste of time)

④ Duo is both too strict and too loose.

In the first example, I selected the words for "to not like" rather than "hate" and was marked incorrect.

In the second, Duo didn't even provide the most correct word (좋아해요), just the common but less correct one.

These things can be completed fixed, even without modifying their algorithm. How?

A "correct override" button that overrides Duo's marking. If I got the right answer but didn't focus on English grammer, I could manually mark as correct.

Any serious language learners already self-mark and self-correct using other learning tools (like Anki).

"Correct override" would also help when a user makes a typo, or clicks the wrong button by mistake, or simply wants to think of the answer without inputting it.

Five seconds after starting with @Lingodeer and I already see an Ignore Spacing option! Customization like this is necessary for optimizing individual learning styles. (In this case, focusing on language production instead of grammar.) 감사감사