We typically assume that the languages spoken among the various Hyborian peoples is based on a common tongue, probably an old Bori tongue, agreed?
Would you speculate that this is similar to Latin being the root with the Romance Languages: Spanish, Portuguese, French, Italian, and so on.
Or, would you speculate that the languages used by Argosseans, Zingarans, Aquilonians, Gundermen, Bossonians, Hyperboreans, Corinthians and the like are languges that are as different as English, German, Spanish, etc.?
And, if you speak one Hyborian language, are you likely to understand and somewhat speak other Hyborian tongues?
Your speculation is...?
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Since English, German and Spanish are all Indo-European languages, the Hyborian tongues are probably similarly related. Also, I assume that the languages of the Hyborian Age in general are similar if not identical to historical languages, because they use many of the same names from actual history, with only slight variations at best.