Translation:He speaks very fast. I do not understand.
I lived in China for 5 years and 明白would be used if you don't understand a situation or context. 听不懂 is what is commonly used if you can't understand what someone is saying to you. So, if you are actually going to China, use "ting bu dong."
Actually, 明白 is made of the two characters "bright" and "white", like saying it is perfectly clear to me and there is that 听 character in 听不懂 which means to hear so that would make sense
'really' should be an acceptable alternative to 'very' in this sentence.
It is a particle. It basically shows that someone is able to use a skill. You'll find it used after the verb (Verb + 得). [Disclaimer: 得 has other uses, so look out for them in the future.]
做 得 很 好 - zuò de hěn hǎo - do 得 very well
说 得 太 快 - shuō de tài kuài - speak 得 too fast
开 得 很 快 - kāi de hěn kuài - drive 得 very fast
To expand on LazyEinstein's comment, one of the uses of 得 (according to my dictionary) is "used between a verb and an adjective or a clause to indicate degree or extent", as shown in the above examples.
If you go to this website: https://www.mdbg.net/chinese/dictionary?wdqb=hello and paste in 得, you'll see the three different meanings/uses for this character.
I don't think "明白" would really be used. I think it is more used for "to recognize".
"do not" and "cannot" or "can not" are semantically and pragmatically the same in this context. The 不/會/能/可以 difference is strict in Chinese, but not in English.
It seems better to say "我听不懂"? "我不明白“ would be more like not apprehending something, no?
I translated it as "so fast" instead of "very fast" (Duolingo didn't accept it). That's the same thing, right?
Why can't I put 她 instead of 他? They sound the same, so shouldn't they both be accepted?
So 很 means very when used after 得, but otherwise just indicates that an adjective is following?
"he speaks very fast i do not understand" me while studying this language lmao but naw i'll get there
Semantically speaking, shouldn't it translate to: "He speaks very quickly, I do not understand." "Fast" isn't an adverb, but in the answer it's referring to "speaks". I understand that the literal translation of "快" is "fast" but in the context of this answer, isn't it grammatically incorrect in English?