Why do you need to distinguish them?
Normaly you know which one is it by seeing the letter in its context : Vietnamese is very different from the other language who use this interdental consonant
Was't it said before anyway that for the catalogue we should only use lettering and names clearly understandable by anglophones?
Currency names should be easy for everyone to write and read. Same goes for rulers name.
Im pretty sure the Numista catalogue guidline show this rule.
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