"If you speak English, I cannot understand that."

Translation: Se vi parolas angle, mi ne povas kompreni tion.

[ActualGoat]

What's the difference between la angla kaj angle?

[Lohnesinpr]

se vi parolas anglan mi ne konprenas tion I do not understand why it is wrong. If you speak English is present tense. I do not understand that is also present tense.

[polyglot928]

The original sentence is "I CANNOT understand that", so you need to add the verb "povas", which indicates the ability to do something, before the verb "konprenas". Also, you need to change "konprenas" to "konpreni" (the infinitive form of "konprenas") since it immediately follows another verb.

I hope that helps ;)

[teachinjos]

I wrote exactly the same and it was wrong. But reading above, it appears duolingo want to express 'speak in English', which hasnt been explained before.

[stevenvarner]

The sentence has two errors: You do not just say "anglan." You must either use the adverb "angle" or the object-noun "la anglan". You must include the article "la." Secondly, as lingo928 pointed out, the phrase includes "cannot understand", which is "ne povas kompreni." However, I think it is perfectly fine Esperanto to just say: "mi ne komprenos tion" (future tense: I will not understand that).