@Kaisermutt You do have -o nominatives in latin in the third declension: "virgo", "Varro", "cicero", "ordo", "sermo"... AFAIK all of these come from the elision of the final -n- of the stem. But yes, the latin word would have been "linguistica", short for "ars linguistica" (
linguistic science, with "ars" a feminine), or a variant of the adjective "linguisticus, a, um". A more proper Latin title would have been something like "de linguis extraneis" .
Both volitional and hortative are used in linguistics, but they mean different things.
Volitional modality is sometimes contrasted with alethic modality ("what you wish to be true" vs. "what is true"). You also find it used to describe constructions like "want to" in English, or specific grammatical moods like the optative or desiderative.
"Hortative" is generally used to describe a mood that contrasts with the imperative. It comes from latin "hortor" for
to encourage; so the rule fo thumb is that it's used when "the speaker encourages someone else to do something". Sometimes it's used as "imperative mood that also has a third person form". In contrast, the Japanese volitional doesn't always imply that you want someone else to do it, e.g., 手伝いましょうか.