Learn Italian: Vorrò seguire una dieta severa. - I will want to follow a strict diet.

Volere (to want) is one of a few irregular verbs that drop a vowel in their future tense stem, which creates a double R. Instead of following the regular pattern, the stem becomes vorr-. Add the first-person singular ending -ò, and you get vorrò (I will want). Other verbs that do this include bere (berrò) and venire (verrò).

Why is seguire left in the infinitive here?

Just like in the present tense, when you have a helping verb like volere followed directly by another verb, only the first verb is conjugated. Since vorrò is already conjugated to show who is doing the action and when, seguire stays in its dictionary form (to follow).

Does severa mean severe or strict?

It can mean both depending on the context! When talking about a diet, a set of rules, or a teacher, severo or severa translates best to strict. Because it describes the feminine singular noun una dieta, the adjective takes the feminine singular ending -a.

Is it common in Italian to say I will want (vorrò) instead of just saying I want (voglio)?