Lacking that technical knowledge, most of us make up names that are pseudo-medieval English-sounding names. Nowadays, when I write fantasy novels, I try to pick names that are not so weird that they will distract readers. I think people will accept a Jeren, but they might get eye strain with a Jhaereihn. Jeren is an example of a name that sounds like it could be an archaic English name.
For my novel, Garden of Dust and Thorns, I decided to go a slightly different route and use a different culture and language as inspiration for names. To that end, many of the names are Tamil names, or at least variations of Tamil names. What is Tamil, you say? Ah, well, the Tamil people are an ethnic group that lives primarily in southern India and northeastern Sri Lanka. They have an ancient and interesting history, culture, and language. Go look them up and read more. I won't get into it here.
However, I did want to share some of the character names from the novel along with their Tamil origins. If you've read the book, you might find the name meanings thematically significant.
Adhi - can be a boy's or a girl's name, sometimes spelled Aadhi - means "the beginning of everything"
Kathiri - from Kathir - means "sun rays" or "divine rays"
Appan - from Tamil word Appa, meaning "Father"
Maranam - a Tamil word meaning "death" or "mortality"
Innpan - A Tamil boy's name meaning "happiest person"
Magesh - Tamil boy's name, related to Mahesh - means "a great ruler"
Anyway, that's just a few to give you an idea. To be honest, I used to agonize a little bit over fantasy names, and my early unpublished stories are full of people and places with unwieldy names. For example, I once wrote a long, ponderous novel about a boy name Trapelo Namikyi and his sidekick, Ruantis. Chew on those names for a bit. Simple names that sound like they could co-exist in the same world work best, but it's fun to take inspiration from the many languages and cultures around the world.