Some languages are more efficient than others as far as number of syllables per meaning.

English is usually efficient, but not particularly so with numbers. For example, 77 (seventy-seven) uses 5 syllables, and 1,000 (one thousand) needs 3.

FingerNumbers

So what is the largest number with only one syllable?

In English it’s 12 (twelve)
In German it’s also 12 (zwölf) 
In French it’s 1,000 (mille)
Finally, in Spanish it’s also 1,000 (mil)