There's very little in the way of examples of less-popular languages in D&D such as Aquan, Kuo-toan, and Undercommon. To give barks to monsters who don't speak Common, I wrote a script to generate phrases from a list of vocabulary for each of the races.
In this example, I have them speaking 75% of the time just to show the variety of phrases they can speak, but in actual gameplay I would have the barks appear at a lower frequency.
The group of sahuagins is speaking my representation of Undercommon, the water elementals are speaking my representation of Aquan, and the kuo-toas are speaking my representation of the Kuo-toan language. The languages are made of whatever real examples I could find (such as suggested common names), as well as online words from other sources, and my own words based on the descriptions of how the languages sound.
The way this is set up, I can easily add pre-made phrases to their list, or alternate language possibilities for creatures that typically speak more than one language.