Rather than codifying an entire language, which - frankly - would be a lot of work and not that much of an addition to the story, I made up the concept for the language and included a few of the words and terms in the dialogue. Mostly, when the characters are speaking the other language, I switch to italics so that the reader knows the characters are conversing in something besides English.
In my Eridani stories, the Eridani language is set as a melodic form of speech. The various nuances of a given concept are expressed by how the word is sung, as described in this excerpt from the first book in the series, The Eridanus Dream
It was an exquisite feast, and even Rory suspended his fears long enough to enjoy the delicacies offered to them. Whatever might happen to them in the village, at least they’d enjoy some good meals during their stay. After they’d finished eating (much too soon in the eyes of the villagers, who all seemed determine to coax the visitors into at least one more morsel), Sean shifted over next to Alice and spoke hurriedly.
“I’m going to give you a quick primer on the local language, and I hope you can pass it on to the others. Y’La and I may not always be close by to help out with translation, so the more all of you learn, the easier it will be.”
“I was thinking the same thing,” she said. “I know you had no control over it, but when they led you off earlier, we were all kind of lost as to what we were supposed to do.”
“I was a bit lost too; they had Y’La and I too far separated for me to benefit from her knowledge, so I had no clue what was going on, either. I couldn’t understand most of what was being said without her nearby. Anyway; here’s some insight that should help with your grasp of the language. Their vocabulary is much more compact than English. Where we have numerous words which mean similar things, depending on connotation and usage, they have one word which covers all nuances. The application of the word is conveyed by how it is sung; the notes associated with the word tell the listener not only the application of the word, but such things as time-tense as well. ‘I went’, ‘I am going’, and ‘I will go’ are all the same word, just sung differently.”
“That’s going to be confusing.”
“It’d be more confusing if you didn’t already know that was how it worked. You’ll need to pay attention to that as you listen, but coming from how we speak, we’d not think that was important. I think you’ll pick it up quickly anyway, but it’s going to take some getting used to for all of you to think of singing your sentences.”
“I certainly hope they’re not music critics.”
“I don’t think you’ll need to worry about that. Now, verbs; personal pronouns are part of the verb conjugation. You’ve heard Y’La say ‘Be’tra’ for ‘thank you’. Using that as an example, the first vowel sound is the object of the action, while the vowel sound at the end indicates who or what is performing the action. The ‘ah’ sound is the first person singular. The ‘ay’ sound is second person singular; ‘you’. ‘Be’tra’ is ‘I thank you’; ‘Ba’tre’ would be ‘you thank me’. The third person singular is the ‘oo’ sound. ‘Bu’tra’ would be ‘I thank him or her or it’. If you add the ‘ee’ sound to the other vowel sound, you make it plural. ‘Be’trai’ would be “We thank you’; ‘Bui’tra’ would be “I thank them’. Are you with me so far?”
“I think so, though this is a lot to try and absorb at once. I should be taking notes.”
“I’ll write this down for you a little later, but I think hearing it first will help. Now, leaving the first vowel sound off makes it a little different concept. For instance, Y’La’s father was thought to be sterile. When Y’La was born, he felt vindicated, and hence her name, which means essentially ‘my proof’ or ‘my vindication’.”
“Okay, I think I’ve got that.”
“However, you have to make sure you sing it correctly. Depending on how you sing her name, it could mean that, or it could mean ‘my acquittal’, or ‘my confirmation’, or ‘my approval’ or even ‘my exoneration’. They’ve embraced an economy of words in favor of a much more expressive system of inflection.”
“I guess our work is cut out for us, then.”
Additionally, in writing out the words, I went with the basics of written Spanish for the phonetics, so that the vowel sounds remain constant in the written Eridani in the story. When writing out translated Eridani in the dialogue, one of the rules was that there would never be a contraction in the Eridani speech. In doing this, I think I was able to create a feel for an alien language, without having to devote countless hours to a lexicon that most readers would simply gloss over if I used it too much. We want to make sure that our stories continue to flow, and if the reader cannot understand too many of the words, we're going to bog them down.