Eleven and Twelve

What is it about these 2 numbers? Why are they not teens?

As in 12 should be twoteen and 11 oneteen.

Another example is the german: Zwolf, elf; Zweizehn, einzehn

I believe this is true for most indo-european languages (apart from italian strangely).

>>2
>>6
They're contractions from the Latin ūndecim (ūnus 'one' + decim 'ten') and duodecim (duo 'two' + decim 'ten').  Just as they are in all Romance languages, aside from Italian, Sardinian, and Romanian, where they are not contracted.

And French is from Vulgar Latin.  Old Frankish was a substratum, but not where the language came from.  Further, eleven and twelve in French didn't come from Germanic roots, they came from Italic roots.