The two major European Germanic languages (German & English) share a similar pattern. Eleven means "one left (over)" and twelve means "two left (over)". The next seven numbers follow the pattern of "x + ten".
The major European Romance languages share a flexible pattern. Each number set begins with the "x + ten" pattern and ends with the "ten + x" pattern, but the point of transition varies. In Spanish and Portuguese, the transistion occurs after fifteen, but in Italian and French, it occurs after sixteen. Curiously, Latin (the root of all Romance languages) follows the "x + ten" pattern from eleven to seventeen and then transitions to "two from twenty" for eighteen and "one from twenty" for nineteen.
Germanic
English
11: eleven, "one left (over)"
12: twelve, "two left (over)"
---
13: thirteen, "three + ten"
14: fourteen, "four + ten"
15: fifteen, "five + ten"
16: sixteen, "six + ten"
17: seventeen, "seven + ten"
18: eighteen, "eight + ten"
19: nineteen, "nine + ten"
German
11: elf, "one left (over)"
12: zwölf "two left (over) "
---
13: dreizehn, "three + ten"
14: vierzehn, "four + ten"
15: fünfzehn, "five + ten"
16: sechzehn, "six + ten"
17: siebzehn, "seven + ten"
18: achtzehn, "eight + ten"
19: neunzehn, "nine + ten"
Romance
Latin (included as a reference)
11: undecim, "one + ten"
12: duodecim, "two + ten"
13: tredecim, "three + ten"
14: quattuordecim, "four + ten"
15: quindecim, "five + ten"
16: sedecim, "six + ten"
17: septumdecim, "seven + ten"
---
18: duodeviginti, "two from twenty"
19: undeviginti, "one from twenty"
French
11: onze, "one + ten"
12: douze, "two + ten"
13: treize, "three + ten"
14: quatorze, "four + ten"
15: quinze, "five + ten"
16: seize, "six + ten"
---
17: dix-sept, "ten + seven"
18: dix-huit, "ten + eight"
19: dix-neuf, "ten + nine"
Spanish
11: once, "one + ten"
12: doce, "two + ten"
13: trece, "three + ten"
14: catorce, "four + ten"
15: quince, "five + ten"
---
16: dieciseis, "ten + six"
17: diecisiete, "ten + seven"
18: dieciocho, "ten + eight"
19: diecinueve, "ten + nine"
Portuguese
11: onze, "one + ten"
12: doze, "two + ten"
13: treze, "three + ten"
14: quatorze, "four + ten"
15: quinze, "five + ten"
---
16: dezesseis, "ten + six"
17: dezessete, "ten + seven"
18: dezoito, "ten + eight"
19: dezenove, "ten + nine"
Italian
11: undici, "one + ten"
12: dodici, "two + ten"
13: tredici, "three + ten"
14: quattordici, "four + ten"
15: quindici, "five + ten"
16: sedici, "six + ten"
---
17: diciassette, "ten + seven"
18: diciotto, "ten + eight"
19: diciannove, "ten + nine"