I roughly translated a name for myself. It would be my nickname, username everywhere. The word is "greyshield". Please don't ask why! So my rough translation for that is "Miththandir" but I don't know if there is a spelling rule for the "thth" part. Please somebody who knows this would give some advices for that. Is it right how I wrote it down or not? Thank you for all of your answers!
looking at the phonetic development rules in Sindarin where two such consonants ('voiceless spirants') meet, it looks that they would be simplified into a single th (reference: http://eldamo.org/content/words/word-1206014597.html. So the name would probably become Mithandir.
[Edited on 11/06/2017 by Tamas Ferencz]
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