Translation:It is very delicious.
"たいへんまずい" sounds weird to me. まずい and たいへん don't match. Since we rarely frankly say "まずい(disgusting)" in a polite way. If you want to politely say that the food isn't good, "あまりおいしくないです(ね)。" sounds better. If you really don't like the food, "全く(全然)(at all)おいしくないです(ね)。". If you want to use "まずい", it's never polite and it's rather too casual. So don't mix it with たいへん and just consider informal ways like "まずい!(rude)", "まず過ぎ(too disgusting)(rude)". These sound rude anyway... If I'm to use たいへん to say that the food isn't good, I'd say "たいへんな味がしますね(meaning, It tasts awful.)", "たいへんな食事でした...(past tense, meaning The meal was awful)" or "あの料理はたいへんですよ...(That dish/meal is awful/crazy)". Or even, "(この料理の)中身が大変なことになってますよ!("Something crazy is happening inside the food!" when the food is rotten and you open it...)". However, these may sound funny to some ones... The point is that you may not usually hear たいへん when talking about bad food.
What is the different between たいへん and とても? They both translate to 'very', do they not?
I rarely use the word たいへん, it normally just means "trouble".
Like, if you're in class and the teacher says to turn in your assignment, but you forgot to do it, you might think to yourself たいへんだ！ which in this context would translate to "I'm in trouble!" That kind of thing. It's like "trouble is coming", or English's, "Oh, no!".
I almost never use たいへん for "very", even though it's technically correct. It might be personal preference though, I'm sure many people use it that way.
Yeah, I think it's like when you would say in English "He's got mad skills", or "He's crazy good at that" - a normally negative adverb used as an intensifier in order to sufficiently convey how extremely good or delicious or amazing etc something is - ie. to convey a level of intensity beyond that of "very".
I'm pretty sure I've heard my mom (born Tokyo, raises Yokohama) say this. She doesn't say it frequently, but when something is really tasty but unhealthy in large quantities (like these mini pecan pies she makes sometimes), she'll say it and describe them as "danger-pies."
"Very" is a gradable adverb and "delicious" is an ungradable adjective. The two can't go together just as you can't say "it's a bit freezing". Unfortunately "extremely" is also gradable. You can say "extremely hot" but not "extremely boiling". "Absolutely" or "really" are both ungradable adverbs that can go with "delicious".
"Very delicious" sounds slightly strained/unnatural to me, which is why I figured they used "very tasty" elsewhere. "Really delicious" would be mostly ok too. https://english.stackexchange.com/questions/309019/why-are-things-often-very-tasty-but-rarely-very-delicious