The expression (עשרת הדברים) has been translated in various manners. Two of them are the commonest ones: 'Ten Commandments' and 'Ten Words'. As regards the latter, we may say it is a very generic translation. If the final sense of this expression focused on the idea of 'to speak', or, 'to pronounce some words' the Bible writer did would use, for example, אמרות, a noun derived from the MT verb אמר (Jer 38:22), since its meaning is - in its own nature - a generic one.
Instead, the root דבר, from which the noun דברים derived, although it remains inside the general concept of 'to speak', it has an own specific nuance. If, now, we put aside the general and mutual (with אמר) meaning of 'to speak', and similar, what remains? The sense of 'to guide, to route, to direct' (this meaning (among others) can be found (only some examples) in Barnes ('to lead, to guide'), Brown-Driver-Briggs ('to lead away'), Benjamin Davies ('to drive'), Reineccius ('duxit'), Fuerst ('to put together in a row' [I.], 'to drive, to lead' [II.]), Gesenius 'to set in a row, to lead, to guide, to drive'.
So, taking into account this nuance, the expression עשרת הדברים would be rendered: "The Ten Guidelines", or "The Ten Leading Principles". In fact, they weren't compiled to represent specific laws but - rather then - real principles on which the various Torah's laws were relied on.
For example, if Exo 20:17 was a directly punishable specific law, how the Israel's judges did punish its contravening? Can I (embodying a judge of Israel) punish a man for coveting something not his own? If one would say, 'Yes, because I will punish this person when his concupiscence will lead him to steal the object of his desire'. All right, but you will be punishing him not to contravene Exo 20:17 but to contravene Exo 20:15! I can punish an action not a feeling.
So, it is clear that the expression עשרת הדברים:
not indicates mere 'words', neither 'specific laws' (liable to a direct punishment), but a whole of guiding principles a people (Israel) is God-encouraged to follow.
To answer directly to your question (really, they are two questions):
I've made no search to know what translation had used the expression "The Ten Commandments" for the first time, but I can say that the motivation to translate in this manner depends just for the nuance we've discover inside this root, 'to guide, to route, to direct'. Personally, I prefer translate this expression, as I mentioned before, "The Ten Guidelines", or "The Ten Leading Principles".