I figured I would post here, if for nothing else than to get feedback and spur me into fleshing this out even further. While I am in the process of restructuring my own world, from the ground up, so to speak, I had established the basis for a common trade language on my world. Unfortunately much of my notes were lost, and so I'll be working on this from memory.

A trade language is an interesting and ever evolving concept. Miriam Webster has this much to say about it ...
A restructured language (as a lingua franca or pidgin) used especially in commercial communication
Next, for those curious, we have Lingua Franca.
often capitalized : a common language consisting of Italian mixed with French, Spanish, Greek, and Arabic that was formerly spoken in Mediterranean ports
: any of various languages used as common or commercial tongues among peoples of diverse speech
: something resembling a common language
and finally, Pidgin ...
: a simplified speech used for communication between people with different languages
Lets be honest here. We have a whole world, with many peoples separated by natural boundaries over the eons. Over time, these people, whether they are related by species or not, will develop independently of one another. Likewise, those many off-branches, like annoying siblings or cousins, will borrow and adapt from whom or whatever they split off from. Over time, language develops among these peoples, and some will have shared various words in their language, with minor and major adaptations, while those separated by vast natural boundaries (great distances, oceans, mountains etc.) will have developed languages completely different from their distant cousins. As they meet again, and with the passing of time, words and concepts are exchanged among these people, becoming part of the common language. Just look at modern English and how many words, phrases and concepts from other cultures have become part of our every day conversations.

In my world, the idea is simple. While there are several major empires whose ambitions and animosity toward each other is comparable to 16th century Spain, France and England, they speak very different languages. Merchants, unlike empires, really have no qualms with one territory, city state, empire etc. or another, so long as they can make a living. Because of this, over time, an amalgamation of a language took shape, first among the merchants and trading caravans as they dealt with each other, and then spreading among the common folk over time. This monster, over even more time, was simplified and standardized, itself becoming a common language among travelers.

When I thought of this, I eventually had to ask myself a few things. First, what did I want the language to sound like? I decided on something that seemed to flow, but was heavy on consonants and featured double vowels. After getting a bit of a feel for how things sounded, I looked at the words I used, the spellings I had thought up, and asked myself how I would simplify things. I then set about developing an alphabet, first just focusing on the sounds I wanted, the letters that in English produced those sounds, and then finally, set them up in a system similar to the Elder Futhark's Aetts that I called, Khaairo (KH-AE-RHO). I had decided that the number three would be important, referring to an archaic creation myth for my world, involving a "three faced god," or a deity with three aspects. Essentially, three was a number of good fortune. With that in mind, I worked around the concept of three Khaairo sets, consisting of thirteen symbols, making up a total of 39 symbols.

Following my decision of 39 symbols and 3 Khaairo sets with 13 symbols each, I decided to take a long hard look into the Elder Futhark and the reason it was set up as it had been. Eventually, I came to an explanation I rather liked, I believe from two known experts in the study of Norse Runes, Freya Aswynn and Edred Thorsson. The short and sweet of it was, that each Aett had a part in a grand story explaining the runes, while each of the runes carried with them several meanings ... A letter within their alphabet, a concept, and an overall meaning used in divination. I liked this three-fold concept. I liked it a lot and applied a similar concept to my own Khaairo.
With that in mind, the three syllable word, Khaairo now had a three part meaning (Weave/Thread/Gift or Keep = To Keep/Give of the Woven Thread), but we'll get to that in a minute. Each symbol would have a letter, or pair of letters associated with it, indicating the sound made. Likewise, every symbol would have a concept attached to it, for example, in the Elder Futhark, the rune Fehu represents the domestic cow, and is a symbol of communal wealth. Likewise each symbol had a concept of it's own that accentuated the Khaairo. Finally, rather than simply attaching a divination system to the Khaairo, I instead settled on a numerical system that would, later, be tied to it's own system of numerology. What this meant was, Each Khaairo told part of a story, and with each symbol in it's respective Khaairo set, a concept and a number that further accentuated the story. The writing system itself, spoke of a common creation myth among the empires. The writing and language system of the common people and the merchants, was a testament to their faith regardless of what god they worshiped, and in that sense, the act of writing or debate could be viewed as an act of passive worship. More so, this conscious act to tie everything together as I did, had been intended as a learning aid for children in my fictional world, better enabling them to learn the language through association.

Phew ... that was a lot from memory. Now with this up, I can begin rebuilding my "common" language. A few notes on the actual writing system, though. I had chosen a system similar to the Mongolian script, with a few notable differences that, once again, tie into the Khaairo.

Written from the top-down, left-to-right.
Each line is begun with a symbol that seems to intersect every letter in the line -- This is the result of how the symbols are drawn. This symbol represents the actual "Thread" mentioned above.
Few grammar marks, among which are included a full stop and mark to indicate a new word.
The color of ink indicates meanings that otherwise are difficult to portray in the script itself.
Because the letter symbols and the number symbols are the same, the left side of a "thread" is reserved for words, where as the right side of that "thread" is reserved for numbers.
Words are written in sets of three syllables. There are words longer than three syllables, and these are the result of "expanded concepts", in which one word may not be enough to get the idea across, thus two or more are strung together.

That's all for now. Hopefully, I'll have more in the coming days for anyone's viewing pleasure and critique. Hopefully some pictures, too.