De or het sterling?

The correct Dutch article is:

de sterling

Rule Words ending in -ing: almost always de. See the rule
Meaning (Dutch) 1. (numismatiek) naam van een munt 2. aanduiding dat het gaat om de volle som (pond sterling)

How to use sterling

the sterlingde sterling
this sterlingdeze sterling
that sterlingdie sterling
our sterlingonze sterling
your sterlingjouw sterling
every sterlingelke sterling
which sterling?welke sterling?
a big sterling / the big sterlingeen grote sterling, de grote sterling

Dutch words ending in sterling

westerling | oosterling | kloosterling

In compound words, the last part decides the article. See the rule

Meaning, plural, diminutive, pronunciation and translations: WikiWoordenboek (Dutch Wiktionary) (CC BY-SA 4.0). Example sentences: Tatoeba (CC BY 2.0 FR).