it depends on the topic; style of writing, and translation.
[for alphabetic language, one word might contain numerous characters, while for ideographic language, one word = one character]
when classical chinese is longer
"traduttore, traditore" (to translate is to betray) - 迻譯即背叛 ⋯ 2 vs 5 words
nautical terms, such as cutter, ketch, schooner; in which, one can grep its meaning and form an mental image directly.
in classical chinese, the word is longer
cutter - 雙頭帆小船 ⋯ 1 vs 5 words
ketch - 高前桅雙桅帆船 ⋯ 1 vs 7 words
schooner - 高後桅雙桅帆船 ⋯ 1 vs 7 words
or, buddhism terms, such as:
अनुत्तरा सम्यक् सम्बोधि (anuttarā samyak sambodhi)
- 阿耨多羅三藐三菩提 ⋯ 3 vs 9 words
bhūtânityatā - 諸行無常 ⋯ 1 vs 4 words
bhūtânātmatā - 諸法無我 ⋯ 1 vs 4 words
śāntaṃnirvâṇam - 涅槃寂靜 ⋯ 1 vs 4 words
when classical chinese is shorter
well, chinese poem should be the shortest, amongst any languages.
taoism related text is, also. e.g. in 周易參同契:
cutting down by metal, the wood prosperous; three, five and one. (frankly, i don't think this book is "translatable"; i just give a word-to-word translation here, omitting background knowledges, assumptions; and implications)
now, 8 classical chinese word vs 11 english words.
when a lengthy document or a book is translated into different languages, will the classical Chinese be the shortest translation
imo, again, it depends on the topic; style of writing, and translation.
have fun :)