"They are Romanian."
In Romanian, the adjective agrees in gender and number with the noun that it describes.
M./N. SG. | Banul/stiloul este românesc. = The coin/pen is Romanian.
M./N. PL. | Banii/stilourile sunt românești. = The coins/pens are Romanian.
F. SG. | Cartea este românească. = The book is Romanian.
F. PL. | Cărțile sunt românești. = The books are Romanian.
M. | Ion este român. = Ion is Romanian.
F. | Maria este româncă. = Maria is Romanian.
PL. M.+M. or M.+F. | Ion și Maria sunt români. = Ion and Maria are Romanian.
PL. F.+F. | Maria și Ioana sunt românce. = Maria and Ioana are Romanian.
They are different inflexions of the adjective românesc:
românesc is for masculine singular:
El este românesc = He is Romanian
românească is for feminine singular:
Ea este românească = She is Romanian
românești is for plural of both genders:
Ei/ele sunt românești = They are Romanian
In Romanian it also matters whether you are talking about a person being a Romanian or about a thing being Romanian.
So when talking about someone being Romanian, you say:
- He is Romanian would be (El) este român
- She is Romanian would be (Ea) este româncă
- They are Romanian would be (Ei/ele) sunt români
Similarly, though there is no clear rule to follow, it differs from a case to another, we have:
- English would be englez / englezoaică / englezi / englezoaice
- French would be francez / franțuzoaică / francezi / franțuzoaice
- Danish would be danez / daneză / danezi / daneze
- Cuban would be cubanez / cubaneză / cubanezi / cubaneze
Yet when talking about things being Romanian, you say:
- It (masculine or neuter) is Romanian would be (El) este românesc
- It (feminine) is Romanian would be (Ea) este romanească
- They are Romanian would be (Ei/ele) sunt românești
Similarly, we have:
- It (masculine or neuter) is English would be (El) este englezesc
- It (feminine) is English would be (Ea) este englezească
They are English would be (Ei/ele) sunt englezești
It (masculine or neuter) is French would be (El) este franțuzesc
- It (feminine) is French would be (Ea este) franțuzească
- They are French would be (Ei/ele) sunt franțuzești
Yet for Danish and Cuban, you describe things in the same manner as people.
Even native Romanian get these wrong sometimes.