The language is officially called "Orte", based on "Orte Empire".
In the original manga, it appears only in written form with Japanese translation (no transliteration/spoken form). The character looks like a random scribble (and even like this...), but later was thought to be a modified Japanese hiragana & katakana.
From 佐とさん's Twitter
When Drifters got animated, Kouta Hirano (the author) didn't think about it at all. He mentioned it on the Twitter,
The incoherent character that I wrote randomly on the spot, known as Orte language, was adjusted to be a fictional Latin-based language by the anime staffs. I can only say sorry while dogeza-ing with my head thrusting the ground.
Seiichi Shirato, a setting researcher for Drifters, also mentioned about the difficulty in dialog speech due to Orte language. From his interview,
What's the most memorable impression when doing researches for Drifters?
The problematic one is about the dialog speech. Regarding the Orte language that is spoken by the elfs, there's a conversation to just reverse the Japanese text/dialog. When we tried it, apparently it's still similar to Japanese, thus we created a language based in Europe. There's an idea to modify Latin little by little, but since Scipio (a character in Drifters) speaks Latin, he would find out!
Surprisingly, Orte language seems to have its own language structure. A Japanese blogger tried to analyze the language, though it ended only until episode 3.
- seda- : stop (verb)
- neruc- : kill (verb)
- quinacos: what (intransitive)
- quinacom: what (transitive)
- tu: you (2nd-person pronoun)
- hi/hii: he (3rd-person pronoun)