In casual conversation you'll hear いいにくい used all over the place. Learn both! 彼女に本当の事を言い かねて彼はだまった He said nothing, it was too hard to tell her the truth. 一年間で浪費するはした金がいくらになるか、だれにも決めかねる。 No one can determine the amount of money wasted in a year.
From a native Japanese teacher I know that にくい is mostly for object characteristics and 難い is for human thinking. So the above comment is not really true.
Snake said > this is just like a stronger version of [gatai] then? e.g. 言い難い - hard to say 言い兼ねる - can't say (because it is so hard to) but i guess, iigatai isn't a verb is it, it's more like an adjective.. how about 'iigatai ga suru' or something (k so i made that up but...^_^)
ii-kaneru seems to have a particularly japanese feeling, something like "well, i don't really want to say that, but... (its true)". Like, I hesitate to say this, but I must. But hopefully a japanese native can clear up the difference some more.
分かりーかねる was also explained as what people at depato stores are taught to say to customers. If someone asks "do you sell X" and you absolutely know you don't sell it, you cannot say that. No, instead it's far better to waste the customer's time and pretend to look for it, and then say "wakari-kaneru" so they don't know. Maybe then they might buy something else while waiting?
いいかねる (not いい兼ねる) and 言い難い has different nuance. The former is subjective, in that you "hesitate to say" whereas the latter means "it is hard to say" and thus principally objective, even though in such expression as 必ずしも言い難い(not necessarily can be said) may not necessarily objective.
thanks! pls review "note" at top...
言い難い is also read as いいにくい。this is more casual than 言いかねる。 こんなこと言いにくいのですが、パーティに来ないでくれませんか。:P
Author: your name
Agree that 言いにくい is more casual in a situation such as こんなこと言いにくいのですが、パーティに来ないでくれませんか = I hesitate to say this, but please don't come to the party.
Formed from Verb -masu base + kaneru Note that kaneru conjugates as a normal verb (e.g. かねた、かねます etc are possible) Vm = Verb -masu base