Term for pronunciation technique

Sometimes there are words that are foreign, and a bit hard for anglophones to articulate. Such as "Dvorak", or "dvelja". When trying to refer to these words in our conversation, sometimes an extra vowel is added between the two consonants, so that it is easier to pronounce. For example, "Dvorak" is pronounced "D-ə-vo-zhak". Also, "bdellium" is pronounced "b-ə-de-llium"

Is there actually a term for this addition of vowel?

This is called epenthesis.

In phonology, epenthesis (/əˈpɛnθəsɪs/, Ancient Greek ἐπένθεσις - epenthesis, from epi "on" + en "in" + thesis "putting") is the addition of one or more sounds to a word, especially to the interior of a word.