Nouns or adjectives that end in –ca and –ga have a hard sound that needs to be preserved in the plural. To do so, the plural forms add an -h, but are otherwise normal in their pluralization. These nouns can be either feminine or masculine.
Singular: la barca
Plural: le barche
Singular: tedesco
Plural: tedeschi
The same addition of the ‘h’ in the plural also applies to nouns ending in –go and in –co. Some nouns ending in –co, however, don’t include ‘h’ in the plural (l’amico - gli amici, simpatico - simpatici).