Translation:It is not good.
The outdated way of reading 良い is えい. Also bear in mind that most (if not all) common Japanese words are usually written in Hiragana only. Here is certainly the case.
I don't know why it became いい from えい, but my guess is for the sake of ease of speaking. It already happens as a syntactic rule when か turns into が, た into だ, etc.
For instance 時時 or also written as 時々 spells ときどき or 神奈川 prefecture spells かながわ where 川 is changed from かわ to がわ.
Or as common pronunciation when for example you drop the 'u' sound in conversation when using です or ます and say 'des', 'mas'.
Consider little etymology lessons sprinkled into your vocab lists. English is an amalgam of Greek, Romantic, Gallic, and Germanic roots.
Historical events like the Crusades and the Jewish Diaspora injected new words with English spellings that tried to approximate Arabic, Slavic, and Hebrew sounds.
Knowing the origin of the word helps us identify the spelling convention. Being able to 'place' a word in time and space gives it context and purpose. It's like filling out the mp3 ID tags in your music folder (does anybody else still do that?) Just taking the time to do it encourages the brain to look for and assign relationships within a seemingly random list.
I think good is "yoi" and to make it negative you have to take off the 'I' and replace it with 'kunai'. We know it does not mean 'often' because there is a 'nai' after.
Furthermore "often" is not an adjective so you wouldn't use "kunai" after it- plus that would make it "yokukunai".
Spelling (written form) and context (spoken + written form.) But since Japanese commonspeech tends to omit a lot of stuff, I can see where confusion would come into play here, especially since "good" and "often" both describe things.
Does anyone know if the kanji for "often" yoku is different from the kanji for "not good" yoku?
it's the same word for both, 良く is more about frequency, the how often does something happens indicates your ability on that stuff, so for example if you say「よく料理する」you are saying that you cook so often that you are already good at it, this is less pretentious than using 上手 in Japanese culture.
So the meaning of よくない "not good" comes from that inference, even to describe things that are not good, if you describe food as よくない is more like saying that is not skillfully done than directly bad.
Thank you for the response! Your explanation really helped me understand the connection between the yoku meanings. :)
Bonus: Had to look up jouzu since I didn't recognize it in kanji form. I kept spelling it "uete." XD Interesting how it means "up hand." Like a high-five!
よく = Good / Fine (i-adjective, connective form)
ない = Not (i-adjective)
です = To be / Is
Already only in Hiragana
In this situation, we have to convert the i-adjective, いい, into connective form (ku-form) so we can add on ない and make it negative.
いい is a weird adjective because before making it into ku-form we have to turn it back into its base/true form, which is よい (yoi). From there, we change the い into く, resulting in よく.
Here you could also add a は (topic particle) after よく which would make it:
This sentence could literally be translated to:
As for (being) good, it is not
However, the は particle also adds contrast to your statement and emphasises the fact that it is not bad. So a rough translation would be:
It isn't bad... (but...)
And then the "(it isn't really good either...)" is sort of implied without actually being said.
The way Duolingo simply translated it was (and I believe makes sense):
It is not necessarily good
いい is the positive i-adjective "good, fine, excellent, sufficient' to describe a noun (can also be written 良い・よい but this is uncommon)
よく is the adverb form to describe a verb "finely, excellently, sufficiently", also used in the conjugation for the negative form よくない "not good, not sufficient, etc."