Will artificial languages help me with anything?

Will they improve my thinking, logic, though process or my communication skills or understanding?

All language learning does, and so do artificial languages. I’d argue that you get to some of the interesting aspects of language learning—such as different approaches to semantics—quicker than you would learning natural languages. OTOH, there are some aspects of natural languages—such as pragmatics, discourse strategies, cultural interplay—which will be either immature or non-existent in most artificial languages. (Though what little there was was one of the most fascinating things for me about artificial language communities.)

I found that trying to communicate in artificial languages helped me think about some aspects of language (semantics, discourse structure) without distraction from other aspects (fricking morphology, culture). Then again, I got a similar epiphany from playing around with Tok Pisin…

Lojban will teach you a fair bit about formal semantics and logic, btw. Like both Jim Grossmann and User said, it’ll teach you less than a PhD in Formal Semantics—though probably as much as an undergraduate course in it.

Why does the Old Testament (in the English versions) use Greek names instead of Hebrew names?

Well, this won’t sound pleasant, but:

The normative version(s) of English, as with most European languages, are culturally influenced by Christianity more than other religions. (Jewish Englishes will in fact use Hebrew names, just as Yiddish does. But standard English unsurprisingly uses Christian forms.)

Christian knowledge of the Hebrew Scriptures was mediated through the Septuagint, the Greek translation of the scripturs—either directly (Orthodox Christianity), or via the Vulgate  (Catholic Christianity). Because of this, English (and most European languages) use Greek versions of the names: Moses (actually Mōysēs in Greek), Jerusalem (Greek Ierousalēm), Solomon (Greek Solomōn). The giveaway is that Greek had no sh sound.

If anything, Protestantism has reintroduced some Hebrew names in the King James Version (and the subsequent traditions), that had been Grecisised/Latinised in Catholicism. Compare the names of books in the Douay–Rheims Bible with those in the King James. Isaiah and Zephaniah are not Greek. Nor is Joshua—although the fact that the Greek for Joshua is Iēsous may have had something to do with that too.

How do Greeks distinguish Jesus from Joshua then? By calling the latter “Jesus, son of Naue”—Naue being the Septuagint version of Nun (biblical figure) .

Why are lots of nicknames/diminutives ended with /i/ sound?

Sound symbolism : the notion that particular sounds are associated with particular meanings or feelings. Not systematically or regularly, but certainly greater than chance. /i/ in particular is associated  with smallness: Ling 131, Topic 5 (session A)  , http://www.linguistics.berkeley…. 

Where does the quote “methinks the lady doth protest too much” come from? What does it mean?

The lady doth protest too much, methinks

As attested in many an online source (and even some offline), Hamlet III.ii, spoken by Gertrude during the play within the play, which Hamlet is using to reenact how he thinks his father was murdered.

The Gertrude-within-the-play is swearing how much she loves her husband; Gertrude outside the play says the actress’ oaths are too effusive (protest = vow). Hamlet, who thinks Gertrude is complicit in Old Hamlet’s murder, responds “O, but she’ll keep her word.”

What is the traditional way to say goodbye in Greek?

Escalating:

Γεια (Health!) or Γεια σου (Health to you): Βye

Αντίο (Italian: To God): Goodbye

Στο καλό (To the good; spoken by the person staying behind): Goodbye, Godspeed

Στην ευκή του Θεού (To God’s blessing, Cretan): Godspeed

Έχε γεια (Have health): Farewell (antiquated)

Καλή αντάμωση (Happy [re-]meeting): Hope to see you again

What is a feminine diminutive?

A diminutive is “a word which has been modified to convey a slighter degree of its root meaning, to convey the smallness of the object or quality named, or to convey a sense of intimacy or endearment”: Diminutive . Well done there, Wikipedia.

So not so much an element of speech, but a modification of a word (typically a suffix), used to convey either that this is a smaller version of the thing, that the thing is cute, or that you like the thing/person.

So, a duck-ling is a small duck. A kitchen-ette is a small kitchen. A beast-ie is a cute beast. Annie-kins is Annie, who you like a lot.

When the cute/dear sense of the ending is dominant, you call it a hypocoristic . That is what is used by linguists to refer to English endings like –ie, which are much more about the cuteness than the smallness.

For the feminine sense, I refer you to Zhenrui Liao’s answer, for languages with grammatical gender. Languages without grammatical gender can still use a suffix just to refer to women. English could have gone that way (brun-ette, bachelorette), but hasn’t (kitchen-ette, leather-ette).

I can’t find it now, but someone on Quora has recently referred to the Australian English ending –ie as a feminine diminutive. Linguists call it a hypocoristic, because it’s much more about the cuteness than the smallness; and I’m not sure it’s even about the cuteness any more. (sickie for sick leave? mozzie for mosquito?)