[dylan604]

With Spanish being similar with distinct words for 11-15 with 16-19 being 10+number. Taking Spanish in high school made me consider that for the first time while never having thought about 11,12 being similar in English until that same thought process.

[shagie]

Latin has 1 to 10 as quite reasonable. 11 is "undecim" (one ten), and 12 is "duodecim" (two ten)... 16 is "sedecim" (six ten), 17 is "septendecim" (seven ten)...

18 is duodeviginti (two from twenty) and 19 is undeviginti (one from twenty).

https://en.wikipedia.org/wiki/Latin_numerals

[anthk]

On_ce, do_ce, tre_ce, cator_ce, quinc_e seem to share similar Latin roots with uno, dos, tres, cuatro, cinco...