i quite know eunjung singing in mandarin only few words need to guess, problem is the lyris, the sentence should more smooth and beautiful to fit this r&b style.
for japanese songs as i dun knew japanese just listen only.
if you had seem the chengdu concert, in encore part they sung ' no.9 ' chinese version but i can't understand at all, so consider that time and little apple, eunjung is improve a lot in her mandarin already.
i also dun knew y, maybe t-ara themself and company has high standard, at least want their chinese as fluent as japanese then will release a full chinese song and even alblum. hyomin before stat that they want their japanese standard like they can live in japan without problem.
actually i dun mind whether they release chinese songs or alblum or not , i dun understand korean and japanese but still love their songs. for me, they just do their best music then is ok to me, no need to consider what language.