Fantasy
A fantasy culture does not need three pages of invented phonetics to feel real. It needs rules.
Who gets a true name. Who is allowed to use it. Who is stuck with a working name because the true one is private, dangerous, sacred, or simply none of an outsider’s business. That is the interesting part. Not whether the vowels are suitably ancient.
The useful trouble starts when someone uses the wrong form of address and thinks it is a small mistake. In some worlds, that would be a social blunder. In others, it is a threat. Much better material, really.
Who gets a true name. Who is allowed to use it. Who is stuck with a working name because the true one is private, dangerous, sacred, or simply none of an outsider’s business. That is the interesting part. Not whether the vowels are suitably ancient.
The useful trouble starts when someone uses the wrong form of address and thinks it is a small mistake. In some worlds, that would be a social blunder. In others, it is a threat. Much better material, really.