yeah, you're right.
adjectives and nouns ending in -e turn into -i in the plural (both masculine and feminine).
ex.:
l'uomo francese (the French man=masc.sing.), la donna francese (the French woman =fem.sing.)
gli uomini francesi (the French men= masc. plur.), le donne francesi (the French women)
It's the same for other kinds of adj. and nouns:
adj. FELICE (masc. and fem. sing)/ FELICI (masc. and fem. plur.)= HAPPY
noun IL PIEDE (masc. sing)/ I PIEDI (masc. plur.)= THE FOOT/FEET
noun LA VOLPE (fem. sing,)/ LE VOLPI (fem. plur.) = THE FOX/FOXES
Don't forget to put the verb in the question:
Lei è inglese?
I hope this short explanation can help you! ;-)