I think magickal mottoes can be a key to initiation; but at first they are just statements of your magickal understanding, or self understanding, as that happens to be when you choose it. Later they become refined, and finally "granted" - a name becomes something you grow into rather than out of. Choosing it announces the birth of your magickal self – it’s how you are known “in temple”, whether physical or astral.
I think t.town.troy is right that it should be not your native language. It should be foreign, suggesting the journey you are beginning (even if you don't know the destination).
When I first started on the magickal path, as a teenager, I chose a very pompous name - "Ego Sum Qui Sum" - the Latin translation of the Hebrew "Ehieh Asher Ehieh" (all beginning with Aleph) - i.e. the name God called himself when Moses asked what his name was on Mount Sinai (Exodus 3:14).
Later, at my first real initiation (into the OTO), I shortened it to Aleph-Aleph-Aleph, calling it "Aleph Shalosh" (Three Aleph), both because it was like my first name, and because it was 111, the number of Aleph and the Fool.
At my second initiation, a few years later, I wanted to identify with the 93 current, so I chose "Jack Allah", which adds up to 93 as IAK ALLA, and also coincidentally contains the three Alephs.
About the same time (1987) I saw Crowley himself for the first time in a dream. When I went up to talk to him, he pointed at my chest and said "I know you, you're Spaceboy". Where he pointed on my chest there was a symbol which I had invented for myself when I was about 11 (Saturn and rings lit on one side, dark on the other, and a five-pointed star in the dark half). I took myself much too seriously to adopt "Spaceboy" as a motto. It became a kind of secret motto for myself, one which I did in fact grow into when I finally grew up and stopped trying to be a grown-up.
I didn't get a new name until 1993, when I had begun to rededicate myself to the Great Work in earnest. My lover one morning told me my name was "Zapapaias", and I took it as the first step in understanding how to progress in initation.
Long story short - the crisis or major initiation happened a year later, when I had to make a choice, do something, but didn't know what. I had received a new name that Saturday morning, after a Genesis 32:24-29 experience. It was "Master Murru" - obviously I didn't want to call myself "Master", and I had no idea of what "murru" meant other than that it was vaguely semitic.
My method for going forward was to analyse the name Zapapaias in a Crowley-G.D. Kabbalistic fashion, like that done in the Lesser Hexagram Ritual (Yod-Nun-Resh-Yod... INRI etc.) and by Crowley throughout his life. I came to the conclusion that I was in the last "Apophis" (last “a”) phase of the name Zapapaias, and was going on to the "S". It was Saturday, after all. Saturn is the planet of Binah. The next step became obvious, and I took it with "fear and trembling".
This name "Master Murru" would be the final one in my magickal initiations, although when I understood it I adopted the Babylonian word for "master" (or "lord") - Bel. So it became "Bel Murru" as a name/motto. Master Murru for me corresponds to V.V.V.V.V. for Crowley - he is the Master of the Temple.
Thanks in advance. 
- but actually - it can be a great space to be in. Clean slate, now draw what you WILL.